feat: deliver phase 2 compatibility lab

[ZSeanYves]

Change summary

• Deliver the Phase 2 compatibility laboratory and close the planned evidence gaps.
• Pin Microsoft MarkItDown v0.1.7 fixtures, add strict structural comparison, and classify every observed difference.
• Add OMML/PPTX chart/SVG coverage, CP932 CSV decoding, bounded stdin, and conservative HTML fallback.

Scope

• tools/compatibility/, src/internal/integration_tests/, CLI/source I/O, HTML/CSV routes, CI, docs, ADR, and CHANGELOG.
• Unsupported XLS, binary Outlook MSG, RSS/Atom, URI/web capabilities remain explicit and fail closed.

Risk and ownership

• Risk: R3 (FFI, input boundary, compatibility contract).
• Owners: API/format maintainers; no new external runtime is enabled by default.

Contract and compatibility

• stdin is accepted as - only with explicit --format; file invocations are unchanged.
• stdin is bounded at 512 MiB. Upstream binaries are downloaded to ignored .tmp and SHA-256 verified.
• ADR: docs/adr/0005-phase-2-compatibility-lab.md.

Verification

• native 909/909; JS/Wasm/Wasm-GC 481/481 each.
• local compatibility 28/28; exact upstream corpus 15/15; integration 51/51.
• governance, documentation, manifest, and git diff --check pass.

Checklist

• Generated artifacts and regeneration command: moon info && moon fmt (the source I/O .mbti addition is deliberate for the new CSV fallback helper).
• No Phase 0 immutable baseline files changed.
• Unsupported capabilities and error behavior documented.
• CI is the blocking merge gate.