ui: show fluid results in the viewport with the part, legend and controls

The window built a deformed copy of the model for every results plot,
which drops the geometry surfaces, so after a fluid solve the bracket
vanished and nothing else was drawn.

A fluid step's plot keeps the part as it is and draws the engine's flow
display through it (the same scene as the headless pictures): the
field on a slice, the part coloured by the flow beside it and
streamlines. The legend shows the field with its bands and the cells
of its extremes (Max/Min mark and turn the view to them); the results
panel swaps the deformation rows for the slice's normal and position,
the obstacles' colours, the streamlines and a frame slider, all
running the results.* commands. The status line describes the new
commands.

Part of #193.

ROADMAP.md

@@ -38,7 +38,7 @@ pressure) is a degree of freedom of the existing DOF framework, not a separate s
 | M9 Post-processing and deck readers | Results readers for public formats (Nastran OP2, LS-DYNA d3plot, Abaqus `.fil`); XY and path plots, cuts, display groups, free-body forces; deck readers that keep unknown keywords; mesh convergence studies | planned |
 | M10 Explicit dynamics | Shared element and material kernels with the implicit solver (`fem`); central-difference solver with lumped mass, stable time step, one-point hex8 with hourglass control and nodal-pressure tet4, bulk viscosity, energy accounting (X1 core: done — `fieldcraft-explicit`, `explicit_dynamic` steps with initial velocities, prescribed motion and planar rigid walls, `solve.explicit`/`solve.history`, small-strain linear elastic; bar wave, rigid-wall impact, energy balance and cantilever-period tests); large-deformation materials (X2: done — updated Lagrangian elements, Jaumann/Hughes–Winget and Green–Naghdi/Flanagan–Taylor rates, J2 bilinear/table plasticity, Johnson–Cook strength with heating and damage, erosion; materials gain `plastic`, `damage`, `erosion` with `model.material.plasticity`/`damage`; Dienes shear, rigid rotation, J2 uniaxial and Taylor-bar tests); contact (X3: done — `interaction.contact.pair`/`general`/`find`, segment-to-segment penalty contact both ways with polygon clipping (passes the contact patch test on non-matching meshes), pairs, general (all exterior faces) and self contact, bucket-grid search, deterministic on any thread count, a penalty from the masses and the stable increment that never shortens it, Coulomb friction with exponential decay by a return map, friction on rigid walls, contact energy and friction dissipation in the balance, initial penetrations adjusted or refused; Abaqus `*CONTACT PAIR`/`*CONTACT`/`*FRICTION` and LS-DYNA automatic contacts in the decks; verified by colliding bars, sliding blocks, the patch test and Hertz's sphere impact); hyperelastic materials (neo-Hookean, Mooney–Rivlin, Yeoh) on the shared material point with average nodal pressure tets, and opt-in mass scaling with the added mass reported: done; runs on hex and tet meshes | started |
 | M11 Equations of state and shells | Polynomial, ideal-gas, Mie–Grüneisen, JWL with programmed burn, tabulated; energy coupling; shock verification (Rankine–Hugoniot, Sod, Noh, Sedov); Belytschko–Lin–Tsay shells with self-contact on quad meshes | planned |
-| M12 CFD: lattice Boltzmann | D3Q19/D3Q27 on grids voxelised from the face-tagged surface; TRT, regularised and cumulant collision; interpolated walls, inlets and outlets; LES (Smagorinsky, WALE) with wall models; thermal LBM and conjugate heat transfer with the structure's thermal solver; non-Newtonian viscosity (power-law, Carreau–Yasuda, Cross, Herschel–Bulkley, Bingham) and temperature-dependent viscosity; porous media (Brinkman, Darcy–Forchheimer); multiphase and free surface (M13); validation by the lid-driven cavity, backward-facing step, cylinder wake (Strouhal) and turbulent channel; octree refinement shared with the hex mesher; wgpu backend (deterministic per device, checked against the CPU) (CPU core: done — `fieldcraft-lbm` with D3Q19 TRT and Guo forcing, halfway bounce-back and moving walls, slip and periodic faces, Zou–He velocity and pressure faces, exact voxelisation of obstacle bodies, momentum-exchange forces per face; fluid materials, fluid domains and fluid steps in the model; `model.fluid_domain.*`, `solve.fluid`; verified by Poiseuille channel and pipe, Couette, Taylor–Green decay, sphere-array Stokes drag and mass conservation; Schäfer–Turek 2D-1 as a benchmark) | started |
+| M12 CFD: lattice Boltzmann | D3Q19/D3Q27 on grids voxelised from the face-tagged surface; TRT, regularised and cumulant collision; interpolated walls, inlets and outlets; LES (Smagorinsky, WALE) with wall models; thermal LBM and conjugate heat transfer with the structure's thermal solver; non-Newtonian viscosity (power-law, Carreau–Yasuda, Cross, Herschel–Bulkley, Bingham) and temperature-dependent viscosity; porous media (Brinkman, Darcy–Forchheimer); multiphase and free surface (M13); validation by the lid-driven cavity, backward-facing step, cylinder wake (Strouhal) and turbulent channel; octree refinement shared with the hex mesher; wgpu backend (deterministic per device, checked against the CPU) (CPU core: done — `fieldcraft-lbm` with D3Q19 TRT and Guo forcing, halfway bounce-back and moving walls, slip and periodic faces, Zou–He velocity and pressure faces, exact voxelisation of obstacle bodies, momentum-exchange forces per face; fluid materials, fluid domains and fluid steps in the model; `model.fluid_domain.*`, `solve.fluid`; verified by Poiseuille channel and pipe, Couette, Taylor–Green decay, sphere-array Stokes drag and mass conservation; Schäfer–Turek 2D-1 as a benchmark; results in the viewport and headless pictures: velocity or pressure on a slice, the obstacles coloured by the flow beside them and streamlines seeded upstream, `results.slice`, `results.surface`, `results.streamlines`: done) | started |
 | M13 Fluid–structure interaction | Immersed-boundary coupling of the lattice Boltzmann fluid with the explicit or implicit structure; interface force transfer; sub-cycling; Aitken then interface quasi-Newton coupling; free-surface flow | planned |
 | M14 Blast and impact fluids | EOS-driven fluids in the explicit solver: ALE multi-material or SPH, with fluid–structure contact | planned |
 | M15 Nonlinear implicit core | Newton–Raphson with line search, automatic increments and cutbacks, convergence on force, displacement and energy; geometric nonlinearity (total and updated Lagrangian, large rotations for shells and beams, follower pressure); every `fem` material behind one interface with its consistent tangent (plasticity, damage and thermal strain from the explicit solver reused implicitly); arc-length (Riks) for snap-through; linear buckling (eigen) with preload stress stiffening, and imperfections from buckling modes; nonlinear stabilisation; restart. Verified by the elastica, Lee's frame, the snap-through arch, the hinged cylindrical shell and plastic collapse loads (solids core: done — `nonlinear_static` steps with automatic increments and cutbacks, Newton–Raphson with the consistent tangent, force, displacement and energy convergence and an optional line search; a material point interface (Kirchhoff stress and spatial tangent from F, with history) with St Venant–Kirchhoff and compressible neo-Hookean; total Lagrangian tet4, tet10, wedge6, hex8, hex20 (full and reduced), hybrid hex8/hex20/tet10 by the three-field mixed form, plane strain and axisymmetric elements; follower pressure with its symmetrised load stiffness; Cauchy stress and logarithmic strain, increment history and frames, `solve.nonlinear`; Abaqus and LS-DYNA decks; verified by the patch and objectivity tests, uniaxial stretch, the elastica and tube inflation by a follower pressure (finite-strain Cook's membrane pending its transcribed reference; J2 plasticity on the interface: Simo's exponential return map at finite strain and the radial return at small strain, both with consistent tangents and the return shared with explicit dynamics, bilinear isotropic and kinematic (small strain), tabulated and Johnson–Cook (rate-independent) hardening, hybrid elements included, load paths for cyclic loading, a tangent predictor for path-dependent materials, verified by uniaxial tension to large strain, Hill's thick cylinder (plastic zone and collapse pressure), a cantilever's collapse and the Bauschinger effect, with quadratic Newton convergence; Mooney–Rivlin and Yeoh options (decoupled, hybrid elements), verified in Treloar's three modes and by a stretched tube's inflation; thermal strain by the multiplicative split at finite strain and the additive one at small strain, with temperatures from temperature loads or the step's own conduction, verified by free and constrained expansion and a heated bar held past yield. a supernodal symmetric indefinite LDLᵀ factorization (bounded Bunch–Kaufman within supernodes, inertia) on which Newton continues through indefinite tangents, so nearly incompressible hybrid elements (ν = 0.4999) converge under prescribed displacement; linear buckling steps (linear preload, initial-stress stiffness of solids and 2D elements, block Lanczos in the K inner product, the shifted buckling transformation on LDLᵀ with an inertia count, `solve.buckle`, Abaqus `*BUCKLE`), verified by Euler columns and Bryan's plate; imperfections from buckling modes; arc-length (Riks–Crisfield, cylindrical or spherical) with limit and bifurcation points from the tangent's inertia, verified by the snap-through of a shallow arch. Next: Lee's frame and the hinged cylindrical shell (with shells), the follower pressure's full tangent (LU), incompatible modes (EAS), kinematic hardening at finite strain, shells and beams) | started |