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/src/config.ts

@@ -0,0 +1,25 @@
+/**
+ * Centralized env parsing — validate at startup, fail fast on bad config.
+ * Other modules read from the frozen `config` object instead of process.env
+ * so misconfiguration shows up here, not deep in a request handler.
+ */
+
+import { parseStalenessHours } from "../../lib/env";
+
+function parsePort(raw: string | undefined, fallback: number): number {
+  if (!raw) return fallback;
+  const n = parseInt(raw, 10);
+  if (!Number.isFinite(n) || n < 1 || n > 65535) {
+    throw new Error(`Invalid PORT=${raw}: must be an integer in 1..65535`);
+  }
+  return n;
+}
+
+export const config = Object.freeze({
+  port: parsePort(process.env.PORT, 3001),
+  parkHoursStalenessHours: parseStalenessHours(process.env.PARK_HOURS_STALENESS_HOURS, 72),
+  nodeEnv: process.env.NODE_ENV ?? "development",
+  rateLimitPerMin: parsePort(process.env.RATE_LIMIT_PER_MIN, 60),
+});
+
+export type Config = typeof config;