Public reference tests: analytic and FreeCAD expected values (#310)

The oracle no longer uses Fusion measurements. tests/oracle/<case>/ now holds the 76 recipes
(our own format, with recorded measurements and tool-specific fields removed) and an
expected.json per case:

- 55 analytic cases: closed-form values from tools/oracle-analytic/ (stdlib Python, formulas
  in each case's "method").
- 21 FreeCAD cases: the same recipe built with FreeCAD's public scripting API by
  tools/freecad-oracle/ (an external program, not a dependency), with a reference.stl for 20.

solvecraft-cli oracle compares body count, volume, area, centre of mass, bbox, face counts
where the geometry fixes them, and, against reference.stl, the sampled Hausdorff distance and
the principal moments (spatial.rs from #301). cargo xtask oracle reads tests/oracle, writes
docs/oracle.md with the source of each value, and supports known_failure marks for tracked
bugs. CI runs it on every PR; a manual workflow regenerates the FreeCAD values. step-corpus,
seam normalisation and the through-all emulation, which only existed to compare with Fusion,
are removed.

75/76 pass; 75-sm-bracket-holes is a known failure (#296).


Claude-Session: https://claude.ai/code/session_01RjGw4gA5ZvKrU8MQP6sBgT

Co-authored-by: bherbruck <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>

README.md

@@ -17,8 +17,9 @@ developer guide and command reference; sources in [docs/book](docs/book)), and t
 Linux Flatpak installation needs the Freedesktop runtime from Flathub as well as the
 SolidCraft application feed. See [install and launch commands](https://bherbruck.github.io/solidcraft/guide/getting-started.html#linux-flatpak).
 
-**Status: early but usable for simple parts.** The historical benchmark report records
-76 of 76 reference parts matching volume, area and topology ([docs/oracle.md](docs/oracle.md)).
+**Status: early but usable for simple parts.** 75 of 76 public reference parts
+match their analytic or FreeCAD-computed volume, area, centre of mass and bounding box
+([docs/oracle.md](docs/oracle.md)); the other is a tracked bug.
 These checks do not establish complete geometric or workflow equivalence. Feature coverage
 is tracked in [docs/parity.md](docs/parity.md) and [ROADMAP.md](ROADMAP.md).
 Open work and known bugs are in [GitHub issues](https://github.com/bherbruck/solidcraft/issues),