Add broadcast input mode for multi-session typing

Broadcast mode sends keystrokes from the active terminal to all other
connected sessions simultaneously. Useful for applying the same
commands across multiple servers.

- Toggle via Ctrl+Shift+B keyboard shortcut or broadcast button in tab bar
- Visual indicator: broadcast button pulses red when active
- Only sends to sessions in 'connected' state
- Notification on toggle
- State stored in app state object

frontend/index.html

@@ -128,6 +128,17 @@
                 <!-- Tabs are injected dynamically by JS -->
             </div>
             <button class="tab-new" id="btn-new-tab" title="New Tab">+</button>
+            <button class="tab-broadcast" id="btn-broadcast" title="Toggle Broadcast Mode (Ctrl+Shift+B)">
+                <!-- Broadcast icon (loudspeaker) -->
+                <svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="0 0 24 24"
+                     fill="none" stroke="currentColor" stroke-width="2"
+                     stroke-linecap="round" stroke-linejoin="round">
+                    <path d="M19.69 14a6.9 6.9 0 0 0 .31-2 6.9 6.9 0 0 0-.31-2"></path>
+                    <path d="M22.82 16.18a10 10 0 0 0 0-8.36"></path>
+                    <path d="M1 12s3-7 9-7 9 7 9 7-3 7-9 7-9-7-9-7z"></path>
+                    <circle cx="12" cy="12" r="3"></circle>
+                </svg>
+            </button>
         </div>
 
         <!-- ============================================================

frontend/src/css/tabs.css

@@ -309,6 +309,36 @@
     background: var(--bg-active);
 }
 
+/* -----------------------------------------------------------------------
+   Broadcast toggle button
+   ----------------------------------------------------------------------- */
+.tab-broadcast {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    width: var(--tab-bar-height);
+    height: var(--tab-bar-height);
+    color: var(--text-tertiary);
+    cursor: pointer;
+    flex-shrink: 0;
+    transition: background var(--transition-fast), color var(--transition-fast);
+    border: none;
+    background: none;
+    opacity: 0.5;
+}
+
+.tab-broadcast:hover {
+    background: var(--bg-hover);
+    color: var(--text-primary);
+    opacity: 0.8;
+}
+
+.tab-broadcast.is-active {
+    color: var(--error);
+    opacity: 1;
+    animation: pulse-dot 1.5s ease infinite;
+}
+
 /* -----------------------------------------------------------------------
    Tab overflow indicators (chevrons at edges)
    ----------------------------------------------------------------------- */

frontend/src/js/app.js

@@ -385,6 +385,13 @@ class App {
                 return;
             }
 
+            // Ctrl/Cmd+Shift+B — toggle broadcast mode
+            if (mod && e.shiftKey && e.key === 'B') {
+                e.preventDefault();
+                this.toggleBroadcast();
+                return;
+            }
+
         });
     }
 
@@ -401,6 +408,7 @@ class App {
         this._bindClick('btn-export', () => this.exportProfiles());
         this._bindClick('btn-recordings', () => this.recordings.openBrowser());
         this._bindClick('btn-new-tab', () => this.profileEditor.openNew());
+        this._bindClick('btn-broadcast', () => this.toggleBroadcast());
         this._bindClick('btn-empty-connect', () => this.profileEditor.openNew());
         this._bindClick('btn-empty-quick', () => this.quickConnect());
 
@@ -432,6 +440,28 @@ class App {
         }
     }
 
+    // ── Broadcast mode ─────────────────────────────────────────────
+
+    /**
+     * Toggles broadcast mode — when active, keystrokes are sent to all
+     * connected sessions simultaneously.
+     */
+    toggleBroadcast() {
+        this.state.broadcastMode = !this.state.broadcastMode;
+        const btn = document.getElementById('btn-broadcast');
+        if (btn) {
+            btn.classList.toggle('is-active', this.state.broadcastMode);
+            btn.title = this.state.broadcastMode
+                ? 'Broadcast Mode ON — keystrokes sent to all sessions (Ctrl+Shift+B)'
+                : 'Toggle Broadcast Mode (Ctrl+Shift+B)';
+        }
+        this.notifications.info(
+            this.state.broadcastMode
+                ? 'Broadcast mode enabled — input sent to all sessions'
+                : 'Broadcast mode disabled'
+        );
+    }
+
     // ── Connection lifecycle ─────────────────────────────────────────
 
     /**

frontend/src/js/state.js

@@ -25,6 +25,9 @@ class State {
         /** @type {boolean} */
         this.secretStoreInitialised = false;
 
+        /** @type {boolean} Whether broadcast mode is active (keystrokes to all sessions). */
+        this.broadcastMode = false;
+
         /** @type {Map<string, Set<Function>>} event name → callbacks */
         this._listeners = new Map();
     }

frontend/src/js/terminal.js

@@ -92,6 +92,19 @@ class TerminalManager {
             try {
                 const b64 = btoa(data);
                 window.go.api.Service.WriteSession(sessionId, b64);
+
+                // Broadcast to all other connected sessions if enabled
+                if (this.app.state.broadcastMode) {
+                    for (const [otherId] of this.terminals) {
+                        if (otherId === sessionId) continue;
+                        const otherSession = this.app.state.getSession(otherId);
+                        if (otherSession && otherSession.state === 'connected') {
+                            try {
+                                window.go.api.Service.WriteSession(otherId, b64);
+                            } catch (_) { /* non-critical */ }
+                        }
+                    }
+                }
             } catch (err) {
                 console.error('WriteSession error:', err);
             }