docs: keep notices fresh at commit time instead of a new CI gate

Regenerate THIRD_PARTY_NOTICES.md from a pre-commit job whenever a
manifest, lock file, vendor manifest, or pyproject is staged, and assert
the committed bytes inside the generator spec the test lane already runs.
Drops the separate doc-sync gate: no extra CI process, and a dependency
edit no longer bounces back from CI to rerun a generator.

scripts/run-gates.ts

@@ -472,7 +472,6 @@ function docSyncLeafGates(options: {
     pnpmScript('tool-catalog', 'verify-tool-catalog', { label: 'tool catalog' }),
     pnpmScript('config-catalog', 'verify-config-catalog', { label: 'config catalog' }),
     pnpmScript('persistence-catalog', 'verify-persistence-catalog', { label: 'persistence catalog' }),
-    pnpmScript('third-party-notices', 'verify-third-party-notices', { label: 'third-party notices' }),
     pnpmScript('doc-graphs', 'verify-doc-graphs', { label: 'doc graphs' }),
     pnpmScript('scoped-events', 'verify-scoped-events', { label: 'scoped events' }),
     pnpmScript('markdown-wrap', 'verify-md-wrap', { label: 'markdown wrap' }),