feat: Add real-time queue depth indicator to viewer UI

Implements a visual badge that displays the count of active work items (queued + currently processing) in the worker service. The badge appears next to the claude-mem logo and updates in real-time via SSE.

Features:
- Shows count of pending messages + active SDK generators
- Only displays when queueDepth > 0
- Subtle pulse animation for visual feedback
- Theme-aware styling

Backend changes:
- Added getTotalActiveWork() method to SessionManager
- Updated worker-service to broadcast queueDepth via SSE
- Enhanced processing status API endpoint

Frontend changes:
- Updated Header component to display queue bubble
- Enhanced useSSE hook to track queueDepth state
- Added CSS styling with pulse animation

Closes #122
Closes #96
Closes #97

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/ui/viewer-template.html

@@ -376,6 +376,36 @@
       animation: spin 1.5s linear infinite;
     }
 
+    .queue-bubble {
+      position: absolute;
+      top: -8px;
+      right: -8px;
+      background: var(--color-accent-primary);
+      color: var(--color-text-button);
+      font-size: 10px;
+      font-weight: 600;
+      font-family: 'Monaspace Radon', monospace;
+      min-width: 18px;
+      height: 18px;
+      border-radius: 9px;
+      display: flex;
+      align-items: center;
+      justify-content: center;
+      padding: 0 5px;
+      box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
+      animation: pulse 2s ease-in-out infinite;
+      z-index: 10;
+    }
+
+    @keyframes pulse {
+      0%, 100% {
+        transform: scale(1);
+      }
+      50% {
+        transform: scale(1.1);
+      }
+    }
+
     .logo-text {
       font-family: 'Monaspace Radon', monospace;
       font-weight: 100;

src/ui/viewer/App.tsx

@@ -17,7 +17,7 @@ export function App() {
   const [paginatedSummaries, setPaginatedSummaries] = useState<Summary[]>([]);
   const [paginatedPrompts, setPaginatedPrompts] = useState<UserPrompt[]>([]);
 
-  const { observations, summaries, prompts, projects, isProcessing, isConnected } = useSSE();
+  const { observations, summaries, prompts, projects, isProcessing, queueDepth, isConnected } = useSSE();
   const { settings, saveSettings, isSaving, saveStatus } = useSettings();
   const { stats, refreshStats } = useStats();
   const { preference, resolvedTheme, setThemePreference } = useTheme();
@@ -96,6 +96,7 @@ export function App() {
           onSettingsToggle={toggleSidebar}
           sidebarOpen={sidebarOpen}
           isProcessing={isProcessing}
+          queueDepth={queueDepth}
           themePreference={preference}
           onThemeChange={setThemePreference}
         />

src/ui/viewer/components/Header.tsx

@@ -10,6 +10,7 @@ interface HeaderProps {
   onSettingsToggle: () => void;
   sidebarOpen: boolean;
   isProcessing: boolean;
+  queueDepth: number;
   themePreference: ThemePreference;
   onThemeChange: (theme: ThemePreference) => void;
 }
@@ -22,13 +23,21 @@ export function Header({
   onSettingsToggle,
   sidebarOpen,
   isProcessing,
+  queueDepth,
   themePreference,
   onThemeChange
 }: HeaderProps) {
   return (
     <div className="header">
       <h1>
-        <img src="claude-mem-logomark.webp" alt="" className={`logomark ${isProcessing ? 'spinning' : ''}`} />
+        <div style={{ position: 'relative', display: 'inline-block' }}>
+          <img src="claude-mem-logomark.webp" alt="" className={`logomark ${isProcessing ? 'spinning' : ''}`} />
+          {queueDepth > 0 && (
+            <div className="queue-bubble">
+              {queueDepth}
+            </div>
+          )}
+        </div>
         <span className="logo-text">claude-mem</span>
       </h1>
       <div className="status">

src/ui/viewer/hooks/useSSE.ts

@@ -10,6 +10,7 @@ export function useSSE() {
   const [projects, setProjects] = useState<string[]>([]);
   const [isConnected, setIsConnected] = useState(false);
   const [isProcessing, setIsProcessing] = useState(false);
+  const [queueDepth, setQueueDepth] = useState(0);
   const eventSourceRef = useRef<EventSource | null>(null);
   const reconnectTimeoutRef = useRef<NodeJS.Timeout>();
 
@@ -83,8 +84,9 @@ export function useSSE() {
 
             case 'processing_status':
               if (typeof data.isProcessing === 'boolean') {
-                console.log('[SSE] Processing status:', data.isProcessing);
+                console.log('[SSE] Processing status:', data.isProcessing, 'Queue depth:', data.queueDepth);
                 setIsProcessing(data.isProcessing);
+                setQueueDepth(data.queueDepth || 0);
               }
               break;
           }
@@ -107,5 +109,5 @@ export function useSSE() {
     };
   }, []);
 
-  return { observations, summaries, prompts, projects, isProcessing, isConnected };
+  return { observations, summaries, prompts, projects, isProcessing, queueDepth, isConnected };
 }