chore: add architecture lint ratchets and perf regression thresholds

ESLint allowlists (only to shrink) for DatabaseSync, synchronous fs in src/main and direct window.goodbuddy subscriptions in components, plus a max-lines ratchet for App.tsx; docs demos and vendored scripts are no longer linted. perf:check (or GB_PERF_CHECK=1 perf:app) fails a non-throttled benchmark that exceeds build/perf-thresholds.json. Records the results in the PERF plan.

package.json

@@ -26,6 +26,7 @@
     "test": "vitest run",
     "test:watch": "vitest",
     "perf:app": "node build/run-app-perf.cjs",
+    "perf:check": "node build/check-perf-thresholds.cjs",
     "perf:knowledge": "node build/run-knowledge-perf.cjs",
     "eval:retrieval": "vitest run --config tests/support/knowledge-retrieval-evaluation.ts tests/knowledge-retrieval-metrics.test.ts tests/knowledge-retrieval-evaluation.test.ts",
     "build": "npm run typecheck && npm run build:bundle",