feat: real-time WebSocket metrics broadcaster and UI updates

- New metrics_broadcaster service (410 lines) — background broadcaster
  pushing CPU/RAM/disk/network stats to subscribed WebSocket clients
- WebSocket protocol extended: subscribe/unsubscribe channels,
  get_rrd/get_node_rrd requests with request_id
- main.py: metrics broadcaster started in lifespan, WS message dispatcher
- websocket_manager.py: subscription map support
- templates: dashboard, instance_detail, proxmox_server_detail,
  proxmox_vms, workspaces — real-time charts and UI updates
- auth.py, servers.py, settings.py: minor fixes

backend/app/templates/workspaces.html

@@ -80,6 +80,88 @@
 </div>
 
 <style>
+/* ── Workspace Modal Overlay ────────────────────────────────── */
+.modal-overlay {
+    position: fixed;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    background: rgba(0, 0, 0, 0.65);
+    backdrop-filter: blur(5px);
+    -webkit-backdrop-filter: blur(5px);
+    z-index: 1050;
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    padding: 1.5rem;
+}
+
+.modal-container {
+    background: var(--bg-card);
+    border: 1px solid var(--border-color);
+    border-radius: var(--radius-lg);
+    width: 100%;
+    max-height: 90vh;
+    overflow-y: auto;
+    box-shadow: 0 24px 64px rgba(0, 0, 0, 0.55);
+    animation: modalIn 0.2s ease;
+}
+
+@keyframes modalIn {
+    from { opacity: 0; transform: scale(0.96) translateY(-8px); }
+    to   { opacity: 1; transform: scale(1)    translateY(0);    }
+}
+
+.modal-header {
+    display: flex !important;
+    align-items: center !important;
+    justify-content: space-between !important;
+    padding: 1.25rem 1.5rem !important;
+    border-bottom: 1px solid var(--border-color) !important;
+    background: transparent !important;
+}
+
+.modal-header h3 {
+    margin: 0;
+    font-size: 1.05rem;
+    font-weight: 600;
+    color: var(--text-primary);
+}
+
+.modal-body {
+    padding: 1.5rem !important;
+    background: transparent !important;
+    color: var(--text-primary) !important;
+}
+
+.modal-footer {
+    display: flex !important;
+    justify-content: flex-end !important;
+    gap: 0.75rem !important;
+    padding: 1rem 1.5rem !important;
+    border-top: 1px solid var(--border-color) !important;
+    background: transparent !important;
+}
+
+.modal-close {
+    background: none;
+    border: none;
+    color: var(--text-muted);
+    font-size: 1.4rem;
+    line-height: 1;
+    cursor: pointer;
+    padding: 2px 6px;
+    border-radius: var(--radius-sm);
+    transition: color 0.15s, background 0.15s;
+}
+
+.modal-close:hover {
+    color: var(--text-primary);
+    background: var(--bg-hover);
+}
+
+/* ── Workspace Grid ─────────────────────────────────────────── */
 .ws-grid {
     display: grid;
     grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));