refactor: production-essentials hardening pass

Backend: structured logger, env-validated config, graceful SIGTERM/SIGINT
shutdown, per-IP rate limiter, per-tier scheduler concurrency latch, error
context on previously-silent catches, compiled-JS Dockerfile stage.

Frontend: lib/api.ts consolidates BACKEND_URL with lazy production-required
check, root + per-segment error.tsx / not-found.tsx / loading.tsx,
generateMetadata on park and ride pages, graceful fallback when backend is
unreachable, Plausible script gated on env vars.

Infra: CI runs lint + typecheck + tests on both packages before docker build,
compose adds healthchecks, log rotation, and memory limits; .env.example
documents every variable.

Cleanup: removed empty app/api/parks/ dir and 0-byte root parks.db, moved
wait-times-urls.txt into docs/, dropped an `as any` cast.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/tsconfig.json

@@ -17,5 +17,5 @@
     "sourceMap": true
   },
   "include": ["src/**/*.ts", "../lib/**/*.ts"],
-  "exclude": ["node_modules", "dist"]
+  "exclude": ["node_modules", "dist", "../lib/api.ts"]
 }