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/js/tabs.js

@@ -100,9 +100,12 @@
     setActive(sessionId) {
       this.app.state.setActiveSession(sessionId);
 
-      // Highlight active tab
+      // Highlight active tab and clear activity indicator
       this.tabList.querySelectorAll(".tab").forEach((t) => {
         t.classList.toggle("tab-active", t.dataset.sessionId === sessionId);
+        if (t.dataset.sessionId === sessionId) {
+          t.classList.remove("tab-has-activity");
+        }
       });
 
       // Show corresponding panel, hide others
@@ -425,6 +428,21 @@
       return [...this.order];
     }
 
+    /**
+     * Marks a background tab as having new activity.
+     * Does nothing if the session is currently active.
+     * @param {string} sessionId
+     */
+    markActivity(sessionId) {
+      if (sessionId === this.app.state.activeSessionId) return;
+      const tabEl = this.tabList.querySelector(
+        `[data-session-id="${sessionId}"]`,
+      );
+      if (tabEl && !tabEl.classList.contains("tab-has-activity")) {
+        tabEl.classList.add("tab-has-activity");
+      }
+    }
+
     /**
      * Returns the session ID of the next tab (wrapping round).
      * @returns {string|null}
@@ -488,6 +506,10 @@
       );
       tab.appendChild(status);
 
+      // Activity indicator (hidden by default, shown when background tab has output)
+      const activity = createElement("span", "tab-activity");
+      tab.appendChild(activity);
+
       // Pin indicator
       if (sessionInfo.pinned) {
         tab.classList.add("tab-pinned");