perf(scene): extend viewport scissor to hatch / image / wipeout passes (Phase 1.4)

Wire pass already uses `WireModel.vp_scissor` to clip viewport-projected
geometry to its paper-space viewport rect; hatch / image / wipeout
passes drew across the whole canvas. When a future paper-space path
projects fills/images into a viewport, they would bleed past the
viewport frame.

Add `vp_scissor: Option<[f32; 4]>` to HatchModel and ImageModel
(mirroring WireModel), forward it through HatchGpu / ImageGpu, and add
per-pass `compute_*_scissors` / `set_scissor_rect` machinery. Factored
the wire-side scissor-projection math into a shared `project_scissor`
helper. Field defaults to None at every constructor site — no producer
sets it yet, so this is plumbing for the paper-viewport fill projection
that Phase 1.4 unblocks without changing current visual output.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/modules/home/draw/hatch.rs

@@ -119,6 +119,7 @@ impl HatchCommand {
             color: [0.75, 0.75, 0.75, 0.85],
             angle_offset: 0.0,
             scale: 1.0,
+            vp_scissor: None,
         }
     }
 }
@@ -254,6 +255,7 @@ impl GradientCommand {
             color: [0.30, 0.60, 0.95, 0.80],
             angle_offset: 0.0,
             scale: 1.0,
+            vp_scissor: None,
         }
     }
 }
@@ -402,6 +404,7 @@ impl CadCommand for BoundaryCommand {
                     color: [0.45, 0.45, 0.45, 0.60],
                     angle_offset: 0.0,
                     scale: 1.0,
+                    vp_scissor: None,
                 };
                 return CmdResult::CommitHatch(model);
             }