Add consistent API request logging and a themed 404 page, bump to 0.4.0

Every app/api route handler now goes through withRouteLogging, which logs
a correlated reqId/method/path/status/duration for each request and turns
any uncaught error into a logged stack trace plus a clean JSON 500 instead
of Next's default opaque failure. proxy.ts logs rejected auth attempts, and
instrumentation.ts's onRequestError catches anything that still escapes a
route handler. Also adds a minimal not-found page matching the app's card
styling.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

instrumentation.ts

@@ -1,3 +1,5 @@
+import { createLogger } from "@/lib/logger";
+
 export async function register() {
   // Only the Node.js server runtime touches better-sqlite3; the Edge
   // middleware runtime must never import this module.
@@ -6,3 +8,26 @@ export async function register() {
     runMigrations();
   }
 }
+
+export async function onRequestError(
+  error: unknown,
+  request: { path: string; method: string; headers: Record<string, string | string[]> },
+  context: { routerKind: string; routePath: string; routeType: string },
+) {
+  const log = createLogger("uncaught");
+
+  // Safety net for errors that escape a route handler's own try/catch (e.g. a
+  // bug in code that never reaches withRouteLogging, or a rendering error) -
+  // route handlers wrapped in withRouteLogging already log and convert their
+  // own errors to a JSON 500, so this rarely double-logs the same failure.
+  const digest = typeof error === "object" && error !== null && "digest" in error ? String(error.digest) : undefined;
+  log.error("unhandled error", {
+    message: error instanceof Error ? error.message : String(error),
+    digest,
+    stack: error instanceof Error ? error.stack : undefined,
+    path: request.path,
+    method: request.method,
+    routePath: context.routePath,
+    routeType: context.routeType,
+  });
+}