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>

lib/api.ts

@@ -0,0 +1,46 @@
+/**
+ * Single source of truth for the backend URL used by Next.js server
+ * components. Defaults to localhost in development; throws at *request time*
+ * in production if BACKEND_URL isn't set so a misdeployed container fails
+ * with a clear message instead of silently pointing at localhost. The check
+ * is lazy so Next.js build-time page-data collection doesn't trip it.
+ */
+
+let warned = false;
+
+export function getBackendUrl(): string {
+  const explicit = process.env.BACKEND_URL;
+  if (explicit) return explicit;
+  if (process.env.NODE_ENV === "production") {
+    throw new Error(
+      "BACKEND_URL env var is required in production. " +
+      "Set it to the backend service URL (e.g. http://backend:3001).",
+    );
+  }
+  if (!warned) {
+    warned = true;
+    console.warn("[lib/api] BACKEND_URL unset — defaulting to http://localhost:3001 (dev only)");
+  }
+  return "http://localhost:3001";
+}
+
+/**
+ * Fetch JSON from the backend with a default revalidate window. Returns
+ * `null` on network failure or non-2xx status — callers handle the null
+ * to render a graceful fallback instead of crashing the server render.
+ */
+export async function apiFetch<T>(
+  path: string,
+  options: { revalidate?: number } = {},
+): Promise<T | null> {
+  const { revalidate = 60 } = options;
+  try {
+    const res = await fetch(`${getBackendUrl()}${path}`, {
+      next: { revalidate },
+    });
+    if (!res.ok) return null;
+    return (await res.json()) as T;
+  } catch {
+    return null;
+  }
+}