feat(sections): MasterFormat title-drift + unknown-section findings in the sections listing

[thewrz]

Why

listSpecSections already reports, per CSI MasterFormat section, whether a spec exists in the
database (inDatabase) — half of a MasterFormat alignment audit. The other half is missing:
a spec whose section number matches MasterFormat but whose title has drifted from the canonical
title, and a spec whose section number doesn't exist in the MasterFormat reference at all.
Clients running periodic alignment reviews (masters on a cadence, projects at kickoff) currently
diff titles themselves.

What

• Extend the sections listing (GET sections / MCP list_sections) rows with:
  • canonicalTitle (from spec_sections), actualTitle (from the stored spec),
    titleMatches (normalized comparison: case, whitespace, punctuation).
• New companion signal: specs whose section is absent from spec_sections
  (unknownSection: true on the spec listing row, or a small dedicated rollup — decide in review).
• Normalization rules documented in the test file; genuinely ambiguous title comparisons get
  // KNOWN AMBIGUITY cases rather than silent behavior.

Tasks

• src/db/queries/search.ts (listSpecSections): title join + normalized comparison
• Unknown-section surfacing (listing flag or rollup)
• openapi.yaml same PR; MCP list_sections parity
• Tests: exact match, case/punctuation drift, real drift, unknown section

Acceptance criteria

• A client can produce a MasterFormat alignment report (missing / present / title-drifted /
  unknown-number) from a single listing call, no client-side diffing.