feat: add structured backend logging

Collector failures, service-API errors, WS connection lifecycle, and
config reload/discovery events were previously invisible outside the
browser (or, for a few config/discovery cases, logged with an
inconsistent ad-hoc console.error). Add a small scoped logger
(lib/logger.ts, level via LOG_LEVEL) and wire it through server.ts,
the scheduler, service collector, config loader/effective store, and
the WS server so operators can see failures via `docker logs`.

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

server.ts

@@ -4,6 +4,9 @@ import { attachWebSocketServer } from "./lib/ws/server";
 import { configStore } from "./lib/config/loader";
 import { effectiveConfigStore } from "./lib/config/effective";
 import { collectorScheduler } from "./lib/collectors/scheduler";
+import { createLogger } from "./lib/logger";
+
+const log = createLogger("server");
 
 const port = Number(process.env.PORT ?? 3000);
 const hostname = process.env.HOSTNAME ?? "0.0.0.0";
@@ -14,6 +17,7 @@ const handle = app.getRequestHandler();
 
 async function main(): Promise<void> {
   await app.prepare();
+  log.info("next.js prepared", { dev });
   const upgradeHandler = app.getUpgradeHandler();
 
   configStore.load();
@@ -21,6 +25,7 @@ async function main(): Promise<void> {
   await effectiveConfigStore.start();
   collectorScheduler.start(effectiveConfigStore.get());
   effectiveConfigStore.onUpdate((config) => collectorScheduler.reconcile(config));
+  log.info("collector scheduler started");
 
   const httpServer = createServer((req, res) => {
     handle(req, res);
@@ -39,23 +44,30 @@ async function main(): Promise<void> {
     void upgradeHandler(req, socket, head);
   });
 
-  function shutdown(): void {
+  function shutdown(signal: NodeJS.Signals): void {
+    log.info("shutting down", { signal });
     collectorScheduler.stop();
     effectiveConfigStore.stop();
     configStore.stop();
-    httpServer.close(() => process.exit(0));
-    setTimeout(() => process.exit(0), 5_000).unref();
+    httpServer.close(() => {
+      log.info("http server closed");
+      process.exit(0);
+    });
+    setTimeout(() => {
+      log.warn("shutdown timed out, forcing exit");
+      process.exit(0);
+    }, 5_000).unref();
   }
 
-  process.on("SIGTERM", shutdown);
-  process.on("SIGINT", shutdown);
+  process.on("SIGTERM", () => shutdown("SIGTERM"));
+  process.on("SIGINT", () => shutdown("SIGINT"));
 
   httpServer.listen(port, () => {
-    console.log(`> PulseNode listening on http://${hostname}:${port}`);
+    log.info("listening", { url: `http://${hostname}:${port}` });
   });
 }
 
 main().catch((err) => {
-  console.error(err);
+  log.error("fatal startup error", { error: (err as Error).message, stack: (err as Error).stack });
   process.exit(1);
 });