chore: achieve zero warnings across oxlint and typecheckers (Phase 15)

[k2kirov]

Code Hygiene & Zero-Warning Hardening (Phase 15)

1. Linter & Compiler Zero-Warning State:

   • Added .oxlintrc.json with ignorePatterns: ["**/*.astro"]. Astro template files are separately compiled and validated by astro check during pnpm typecheck (which reported 0 errors, 0 warnings, 0 hints).
   • Resolved all unsafe optional chaining operations across core audit test suites (ugc-trust-boundary-markers.test.ts, table-markdown-round-trip-loss.test.ts, chunk-boundary-referent-integrity.test.ts, section-split-risk-profile.test.ts, ai-usage-signal-coherence-across-channels.test.ts, aipref-content-usage-declaration-validity.test.ts).
   • Fixed unnecessary regex escapes in mcp-tool-contract-validity.ts and dossier-public.ts.
   • Replaced new Array() with Array.from() in ai-catalog-urls.ts.
   • Removed redundant fallback object spreads in server-rendered.ts and options.ts.
   • Cleaned up unused import in content.config.ts.
   • Brought oxlint . down from 136 warnings to 0 warnings and 0 errors across all 687 files.

2. Quality Gates:

   • All 7 quality gates verified 100% green.