Add show improvement features: crossfade, emotions, returning callers, transcripts, screening

- Music crossfade: smooth 3-second blend between tracks instead of hard stop/start
- Emotional detection: analyze host mood from recent messages so callers adapt tone
- AI caller summaries: generate call summaries with timestamps for show history
- Returning callers: persist regular callers across sessions with call history
- Session export: generate transcripts with speaker labels and chapter markers
- Caller screening: AI pre-screens phone callers to get name and topic while queued

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/css/style.css

@@ -593,6 +593,23 @@ section h2 {
 .hangup-btn.small { font-size: 0.75rem; padding: 0.2rem 0.5rem; }
 .auto-followup-label { display: flex; align-items: center; gap: 0.4rem; font-size: 0.8rem; color: #999; margin-top: 0.5rem; }
 
+/* Returning Caller */
+.caller-btn.returning {
+    border-color: #f9a825;
+    color: #f9a825;
+}
+
+.caller-btn.returning:hover {
+    border-color: #fdd835;
+}
+
+/* Screening Badges */
+.screening-badge { font-size: 0.7rem; padding: 0.1rem 0.4rem; border-radius: 3px; font-weight: bold; }
+.screening-badge.screening { background: #e65100; color: white; animation: pulse 1.5s infinite; }
+.screening-badge.screened { background: #2e7d32; color: white; }
+.screening-summary { font-size: 0.8rem; color: #aaa; font-style: italic; flex-basis: 100%; margin-top: 0.2rem; }
+.queue-item { flex-wrap: wrap; }
+
 /* Three-Party Chat */
 .message.real-caller { border-left: 3px solid #c62828; padding-left: 0.5rem; }
 .message.ai-caller { border-left: 3px solid #1565c0; padding-left: 0.5rem; }