Retire legacy reference data and the external command catalog (#302)

- Remove xtask/data/fusion-catalog.tsv and xtask/data/fusion-ids.tsv.
- Remove the legacy command-id table (crates/engine/src/legacy_ids.rs) and its use in
  find_command and in the shortcut, recents and pinned-command loaders. Only SolidCraft's
  dotted ids name commands; any other id is an unknown command.
- Boundary Fill's id becomes solid.boundary_fill.
- Replace the parity report with SolidCraft's own feature checklist: `cargo xtask features`
  writes docs/features.md from the command registry.
- docs/oracle.md, docs/step-import.md (corpus section) and docs/iges-import.md: reference
  results are being rebuilt on analytic and open-source (FreeCAD) values; see #292.
  `cargo xtask oracle` and `cargo xtask step-corpus [--iges]` write these placeholders.
- AGENTS.md, CLAUDE.md, CONTRIBUTING.md, README.md, ROADMAP.md and the book describe
  SolidCraft as independent, with reference tests on analytic values and open-source tools,
  and agents do not drive or extract data from commercial CAD products.


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

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

crates/ui-egui/src/preselect_tests.rs

@@ -543,7 +543,7 @@ fn boundary_fill_finds_the_cells_and_fills_the_ticked_ones() {
         {"command": "solid.box", "params": {"length": 20, "width": 20, "height": 20}},
         {"command": "solid.box", "params": {"length": 20, "width": 20, "height": 20, "corner": [10, 10, 0], "operation": "new"}}
     ]));
-    let mut d = start(&mut app, vec![], "SurfaceSculpt");
+    let mut d = start(&mut app, vec![], "solid.boundary_fill");
     d.inputs[0].items = vec![Sel::Body { name: "Body1".into() }, Sel::Body { name: "Body2".into() }];
     app.dialog = Some(d);
     // The dialog finds the cells on its next frame.