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 <bherbruck@herbrucks.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

docs/book/src/introduction.md

@@ -21,7 +21,7 @@ also script, test or hand to an agent.
 SolidCraft is early. Sketching, solid modelling, parameters, components with joints, sheet metal
 and a plastic-enclosure subset work; surfaces, drawings, CAM and simulation are deferred. The
 [roadmap](https://github.com/bherbruck/solidcraft/blob/main/ROADMAP.md) has the details, and
-[command parity](dev/parity.md) and the [Fusion oracle](dev/oracle.md) measure how far along it
+[command parity](dev/parity.md) and the [reference tests](dev/oracle.md) measure how far along it
 is.
 
 Existing `.solvecraft` designs and `solvecraft-cli` commands keep their names and behavior.