feat: live docker/database widgets over WebSocket (M2)

Adds a custom server.ts (http server + Next request handler + a
noServer:true WebSocket server on /ws) so the app can push live data
without polling. A CollectorScheduler runs one interval-based job per
docker/database widget instance, backed by dockerode against
/var/run/docker.sock, and reconciles jobs when config.yml changes.

Config hot-reload is now fully wired: chokidar watches config.yml/.env,
re-validates on change, and broadcasts config:update (or a
non-destructive config:error, keeping the last-good config) to every
connected browser. The client subscribes to per-widget topics over a
single shared WebSocket with exponential-backoff reconnect and
last-result caching for instant resubscribe.

Verified end-to-end against real throwaway containers (nginx, redis):
live CPU/mem/uptime/health streamed over the socket, interval changes
picked up without a server restart, and a broken config.yml correctly
falls back to the last-valid config instead of crashing the app.

package.json

@@ -3,9 +3,9 @@
   "version": "0.1.0",
   "private": true,
   "scripts": {
-    "dev": "next dev",
+    "dev": "tsx watch server.ts",
     "build": "next build",
-    "start": "next start",
+    "start": "NODE_ENV=production tsx server.ts",
     "lint": "eslint"
   },
   "dependencies": {