feat: add VNC support with noVNC integration

- Introduced a new VNC viewer panel in the frontend, allowing users to connect to VNC sessions.
- Implemented VNC connection handling with optional SSH tunneling in the backend.
- Added a new SSH key manager for managing SSH keys within the terminal.
- Created a trigger rules engine to monitor terminal output and trigger actions based on defined patterns.
- Added CSS styles for the VNC viewer and its components.
- Updated database schema to support VNC protocol in profiles.
- Implemented WebSocket proxy for VNC connections to facilitate communication between the frontend and backend.

frontend/src/css/tabs.css

@@ -163,6 +163,40 @@
   background: var(--text-tertiary);
 }
 
+/* -----------------------------------------------------------------------
+   Activity indicator — pulses when background tab has new output
+   ----------------------------------------------------------------------- */
+.tab-activity {
+  width: 6px;
+  height: 6px;
+  border-radius: 50%;
+  flex-shrink: 0;
+  background: var(--accent);
+  opacity: 0;
+  transition: opacity 150ms ease;
+}
+
+.tab-has-activity .tab-activity {
+  opacity: 1;
+  animation: pulse-dot 1.5s ease infinite;
+}
+
+.tab-active .tab-activity {
+  opacity: 0;
+}
+
+/* Trigger flash — brief glow when a trigger rule matches */
+.tab-trigger-flash {
+  animation: trigger-flash 2s ease;
+}
+
+@keyframes trigger-flash {
+  0%, 100% { background: var(--bg-hover); }
+  15% { background: rgba(239, 83, 80, 0.25); }
+  30% { background: var(--bg-hover); }
+  45% { background: rgba(239, 83, 80, 0.15); }
+}
+
 /* -----------------------------------------------------------------------
    SFTP toggle button — revealed on hover (SSH tabs only)
    ----------------------------------------------------------------------- */