Meshing test corpus built with SolidCraft; assembly placement in open_design (#11)

* geometry: build designs from SolidCraft command scripts (feature scripts)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* geometry: place component bodies through their occurrences when opening a design

An assembly's instances were missing and moved components sat at their own origin.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* Meshing test corpus: 16 SolidCraft recipes, analytic shapes, loader and runner

modelcraft-testkit holds the corpus (tests/corpus/<name>/recipe.json run through SolidCraft's
engine, then opened as a design) and the runner binary behind cargo xtask corpus.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* docs: corpus results, test corpus architecture and the scripts feature; licences

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* corpus: measure each body once, check stage widths, simpler loader and runner

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

tests/corpus/spline-vase/README.md

@@ -0,0 +1 @@
+A vase revolved from a spline profile: doubly curved faces of varying curvature around a closed axis.

tests/corpus/spline-vase/recipe.json

@@ -0,0 +1,9 @@
+{"corpus": {"categories": ["organic"]},
+ "commands": [
+  {"command": "sketch.create", "params": {"plane": "XZ", "name": "Profile"}},
+  {"command": "sketch.line", "params": {"points": [[0, 0], [20, 0]], "ids": ["base"]}},
+  {"command": "sketch.spline.fit_point", "params": {"points": ["base.end", [28, 20], [14, 45], [18, 70]]}},
+  {"command": "sketch.line", "params": {"points": [[18, 70], [0, 70], [0, 0]]}},
+  {"command": "sketch.finish", "params": {}},
+  {"command": "solid.revolve", "params": {"axis": "Z", "body_name": "Vase"}}
+ ]}