Conformance: pin the complete PR-249 reference inventory

[chrisbbreuer]

Parent: #143
Roadmap: #134
Source: oven-sh/WebKit#249 @ 3a14f2a821ac56fcb01d1c765200be7e9dfdb458

Goal

Replace the runtime-only PR-249 reference classifier with a checked-in,
version-pinned, machine-readable inventory that owns every vendored file and
every executable case's promotion/disposition state.

Acceptance

• Every vendored file is represented exactly once and checksummed.
• All 259 executable cases and five helper/preload files have one explicit
  state.
• All 24 reference-only executables name dependencies, required hooks, and
  owner issues without free-form fallback categories.
• The build audit fails on any inventory or classification drift.
• Focused checker tests cover additions, deletions, checksum drift,
  allowlist movement, and missing/stale dispositions.
• Documentation publishes exact totals and reproduction.

Result

docs/.data/pr249-reference-inventory.json
pins 339 files with SHA-256 and size, including 264 JavaScript files: 235
promoted executables, 24 reference-only executables, and five helpers. The 24
blocked cases use 13 stable dependency IDs linked to #143/#144/#145/#146 and
the relevant WebAssembly Threads owners.

zig build threads-reference-audit regenerates the artifact and runs six
drift-detector self-tests. Runtime implementation/promotion stays in follow-up
#143 children by dependency.

[chrisbbreuer]

Completed in feb8e37e.

Evidence:

• 339/339 vendored files represented once with size and SHA-256;
• 259 executable cases: 235 promoted, 24 reference-only;
• five helper/preload files;
• all 24 blocked executables mapped to stable dependencies, exact shell
  hooks/options, and owner issues;
• build-integrated regeneration check passed;
• six focused drift tests passed (addition, deletion, checksum, allowlist,
  missing disposition, stale disposition);
• README gained only one replacement bullet; benchmark scores are unchanged.