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.

lib/format.ts

@@ -0,0 +1,22 @@
+export function formatUptime(seconds: number): string {
+  if (seconds < 60) return `${seconds}s`;
+  const days = Math.floor(seconds / 86_400);
+  const hours = Math.floor((seconds % 86_400) / 3_600);
+  const minutes = Math.floor((seconds % 3_600) / 60);
+  if (days > 0) return `${days}d ${hours}h`;
+  if (hours > 0) return `${hours}h ${minutes}m`;
+  return `${minutes}m`;
+}
+
+const BYTE_UNITS = ["KB", "MB", "GB", "TB"];
+
+export function formatBytes(bytes: number): string {
+  if (bytes < 1024) return `${bytes} B`;
+  let value = bytes / 1024;
+  let unitIndex = 0;
+  while (value >= 1024 && unitIndex < BYTE_UNITS.length - 1) {
+    value /= 1024;
+    unitIndex += 1;
+  }
+  return `${value.toFixed(1)} ${BYTE_UNITS[unitIndex]}`;
+}