Upgrade to mdbase SDK beta.124: drop startup patch, adopt revisioned batches, metadata discovery and file stat

[callumalpass]

• Upgrade (bad86bc): every @mdbase-dev/* package pinned to exactly 0.1.0-beta.124. The temporary beta.123 startup-cancellation pnpm patch is removed, because beta.124 includes the upstream fix (Fix superseded startup assessment cancellation mdbase-connect#557).
• Wave B (5394093), gated on the authority advertising support, with fallbacks:
  • Annotation hydration: revision-bearing batch documents replace one whole-document read per annotation, about 6 round trips for 300 annotations instead of 300 reads. Revisions are kept for editing.
  • Document and collection-file lookups: files.stat replaces folder listings.
  • Discovery: metadata-only query output where only paths, types and selected values are needed.
  • Wave B behaviour is covered in packages/connect/src/wave-b.test.ts.
• Audit fix (cdbcf70): the full browser audit's annotation-workbench "Edit here" failure was a stale expectation. Promoting the annotation closes the sidebar and releases its editor lease, so the audit now expects that. The full audit is green again, which the new SDK consumer canary (Gate SDK publication on exact-tarball consumer canaries mdbase-connect#562) needs.

Validation: pnpm check (1,105 tests); full browser audit (40 scenarios), annotation-only (13) and PDF-touch all pass. The accessibility audit still reports one existing command-palette contrast finding.