Add multi-speaker support for group conversations

Features:
- Speaker management system with unique IDs and colors
- Visual speaker selection with avatars and color coding
- Automatic language detection per speaker
- Real-time translation for all speakers' languages
- Conversation history with speaker attribution
- Export conversation as text file
- Persistent speaker data in localStorage

UI Components:
- Speaker toolbar with add/remove controls
- Active speaker indicators
- Conversation view with color-coded messages
- Settings toggle for multi-speaker mode
- Mobile-responsive speaker buttons

Technical Implementation:
- SpeakerManager class handles all speaker operations
- Automatic translation to all active languages
- Conversation entries with timestamps
- Translation caching per language
- Clean separation of original vs translated text
- Support for up to 8 concurrent speakers

User Experience:
- Click to switch active speaker
- Visual feedback for active speaker
- Conversation flows naturally with colors
- Export feature for meeting minutes
- Clear conversation history option
- Seamless single/multi speaker mode switching

This enables group conversations where each participant can speak
in their native language and see translations in real-time.

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

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

static/css/styles.css

@@ -450,4 +450,110 @@
 /* Smooth text appearance for streaming */
 .streaming-text {
     transition: all 0.1s ease-out;
+}
+
+/* Multi-speaker styles */
+.speaker-button {
+    position: relative;
+    padding: 8px 16px;
+    border-radius: 20px;
+    border: 2px solid;
+    background-color: white;
+    font-weight: 500;
+    transition: all 0.3s ease;
+    min-width: 120px;
+}
+
+.speaker-button.active {
+    color: white !important;
+    transform: scale(1.05);
+    box-shadow: 0 2px 8px rgba(0,0,0,0.2);
+}
+
+.speaker-avatar {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    width: 30px;
+    height: 30px;
+    border-radius: 50%;
+    background-color: rgba(255,255,255,0.3);
+    color: inherit;
+    font-weight: bold;
+    font-size: 12px;
+    margin-right: 8px;
+}
+
+.speaker-button.active .speaker-avatar {
+    background-color: rgba(255,255,255,0.3);
+}
+
+.conversation-entry {
+    margin-bottom: 16px;
+    padding: 12px;
+    border-radius: 12px;
+    background-color: #f8f9fa;
+    position: relative;
+    animation: slideIn 0.3s ease-out;
+}
+
+@keyframes slideIn {
+    from {
+        opacity: 0;
+        transform: translateY(10px);
+    }
+    to {
+        opacity: 1;
+        transform: translateY(0);
+    }
+}
+
+.conversation-speaker {
+    display: flex;
+    align-items: center;
+    margin-bottom: 8px;
+    font-weight: 600;
+}
+
+.conversation-speaker-avatar {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    width: 25px;
+    height: 25px;
+    border-radius: 50%;
+    color: white;
+    font-size: 11px;
+    margin-right: 8px;
+}
+
+.conversation-text {
+    margin-left: 33px;
+    line-height: 1.5;
+}
+
+.conversation-time {
+    font-size: 0.8rem;
+    color: #6c757d;
+    margin-left: auto;
+}
+
+.conversation-translation {
+    font-style: italic;
+    opacity: 0.9;
+}
+
+/* Speaker list responsive */
+@media (max-width: 768px) {
+    .speaker-button {
+        min-width: 100px;
+        padding: 6px 12px;
+        font-size: 0.9rem;
+    }
+    
+    .speaker-avatar {
+        width: 25px;
+        height: 25px;
+        font-size: 10px;
+    }
 }