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>

app/api/health/route.ts

@@ -1,11 +1,16 @@
 import { NextResponse } from "next/server";
 import { sqlite } from "@/lib/db/client";
+import { withRouteLogging } from "@/lib/api/with-route-logging";
+import { createLogger } from "@/lib/logger";
 
-export async function GET() {
+const log = createLogger("health");
+
+export const GET = withRouteLogging("health.check", async () => {
   try {
     sqlite.prepare("select 1").get();
     return NextResponse.json({ status: "ok" });
-  } catch {
+  } catch (err) {
+    log.error("health check failed", { error: err instanceof Error ? err.message : String(err) });
     return NextResponse.json({ status: "error" }, { status: 500 });
   }
-}
+});