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 <[email protected]>

docs/book/src/guide/plastic.md

@@ -10,4 +10,4 @@ The PLASTIC tab has a small enclosure subset:
   clearance per material, used as the features' defaults.
 
 Rib and web (on the SOLID tab) complete the set. These features are checked against
-hand-computed geometry rather than a Fusion oracle.
+hand-computed geometry.

docs/book/src/guide/sheet-metal.md

@@ -11,8 +11,8 @@ The SHEET METAL tab builds parts from a sheet of constant thickness under a **sh
 - **Create Flat Pattern** (`sheet.flat_pattern`) shows the flat part with its bend lines and a
   bend table, and exports it as DXF or a bend-table CSV through the save picker.
 
-Bends follow the rule's K-factor, so flat lengths match what a press brake will make. The
-oracle checks these against parts built in Fusion.
+Bends follow the rule's K-factor, so flat lengths match what a press brake will make. Tests
+check flat lengths against hand-computed bend allowances.
 
 For a shop drawing or spreadsheet, `sheet.export_bend_table` returns CSV by default; choose
 `format: "json"` for structured data. It includes the sheet rule, thickness, bend angles,