docs: generate THIRD_PARTY_NOTICES.md and gate it in doc-sync

Replace the hand-written inventory with scripts/gen-third-party-notices.ts,
verified fresh by a doc-sync leaf gate. Tier by declaring workspace area
rather than manifest section, so test-support runtime declarations stay
dev-only and every mountable plugin's dependencies are disclosed as
runtime; list the pnpm-patched packages; point the Python closure at
uv.lock. Re-record the translation-prompt snapshot the README link
invalidated.

scripts/run-gates.ts

@@ -472,6 +472,7 @@ 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' }),