Add configurable structured logging

Adds a leveled JSON logger (error/warn/info/verbose/debug, controlled via
LOG_LEVEL) wired into the Express API (access log, error middleware,
crash handlers, memory heartbeat) and the Next.js server (page-request
proxy, instrumentation crash handlers, heartbeat). LOG_LEVEL is exposed
through compose.yaml, and both services now rotate their Docker logs
(json-file, 20m x 10 files) instead of growing unbounded. Intended to
capture long-running diagnostic data for the intermittent 502s seen on
the Docker host.

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

src/instrumentation-node.ts

@@ -0,0 +1,25 @@
+import { createLogger, toErrorMeta } from "./shared/logging/logger";
+
+export function registerNodeInstrumentation() {
+  const logger = createLogger("web");
+  const heartbeatIntervalMs = 5 * 60 * 1000;
+
+  logger.info("web server starting", { pid: process.pid });
+
+  process.on("uncaughtException", (error) => {
+    logger.error("uncaught exception", toErrorMeta(error));
+  });
+
+  process.on("unhandledRejection", (reason) => {
+    logger.error("unhandled rejection", toErrorMeta(reason));
+  });
+
+  setInterval(() => {
+    const memory = process.memoryUsage();
+    logger.verbose("heartbeat", {
+      uptimeSeconds: Math.round(process.uptime()),
+      rssMb: Math.round(memory.rss / 1024 / 1024),
+      heapUsedMb: Math.round(memory.heapUsed / 1024 / 1024),
+    });
+  }, heartbeatIntervalMs).unref();
+}