Fleet: Beszel hub integration — rich per-node metrics + per-node monitor (Phase 1)

Tap each node's Beszel metrics (GPU/temps/disk-IO/network/per-container — beyond
our basic heartbeat) by reading the workspace's Beszel hub. The agents run in
WS-only mode with no locally-readable socket, so (per the de-risk) the server taps
the hub's PocketBase API instead of the daemon reading agents — no daemon changes.

- migrations: workspace_beszel (BYO hub URL + login, server-side only, mirrors the
  Tailscale BYO pattern) + node_metrics (latest scalar columns + JSONB blob).
- cm-db: repo/fleet_beszel.rs, repo/node_metrics.rs; nodes SELECT joins node_metrics
  (gpu_pct/temp_max surfaced on node_json for the live cards).
- cm-api: beszel.rs client (auth-with-password, poll `systems`, map to nodes by
  hostname, upsert metrics) + a 15s spawn_poller; routes/beszel.rs (connect/status/
  disconnect + GET /api/nodes/{id}/metrics with history proxied live from the hub).
- frontend: HostCard gains a GPU/temp readout + a Monitor button; NodeMonitor is a
  full-width per-node page (current panel + CPU/mem/GPU/temp/net/disk charts from the
  hub's 1m history); a "Beszel monitoring" connect form in the Local view.

Reachability confirmed: gw-04 → the hub over the tailnet (100.123.224.84:8090). Needs
the user to connect their hub login to activate the poller.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

crates/cm-api/src/routes/nodes.rs

@@ -37,6 +37,8 @@ fn node_json(n: &nodes::NodeRow) -> Value {
         "tailscaleIp": n.tailscale_ip,
         "lastSeen": n.last_seen.map(|t| t.unix_timestamp()),
         "createdAt": n.created_at.unix_timestamp(),
+        "gpuPct": n.gpu_pct,
+        "tempMax": n.temp_max,
         "health": n.health.as_ref().map(|h| json!({
             "cpuPct": h.cpu_pct,
             "memTotal": h.mem_total,