fix: add loading indicator for audio generation buttons

Add visual feedback during TTS audio generation by implementing
Gradio event chaining pattern:

- Disable button and show "Generating..." text on click
- Display runtime progress indicator via show_progress="minimal"
- Restore original button text and re-enable after completion

This improves UX by providing clear feedback during the 3-20 second
audio generation process instead of appearing unresponsive.

app.py

@@ -4869,35 +4869,51 @@ Please try again with different parameters.
         # ============================================================
         # AUDIO BUTTON EVENT HANDLERS
         # ============================================================
+        # Use event chaining to show loading state during audio generation:
+        # 1. Disable button and change text to "Generating..."
+        # 2. Run async audio generation with progress indicator
+        # 3. Restore button to original state
 
         # Analysis audio button
         analysis_audio_btn.click(
+            fn=lambda: gr.update(value="Generating...", interactive=False),
+            outputs=analysis_audio_btn
+        ).then(
             fn=generate_analysis_audio,
             inputs=[],
-            outputs=[
-                analysis_audio_player,
-                analysis_audio_btn
-            ]
+            outputs=[analysis_audio_player, analysis_audio_btn],
+            show_progress="minimal"
+        ).then(
+            fn=lambda: gr.update(value="🔊 Listen to Analysis", interactive=True),
+            outputs=analysis_audio_btn
         )
 
         # Build portfolio audio button
         build_audio_btn.click(
+            fn=lambda: gr.update(value="Generating...", interactive=False),
+            outputs=build_audio_btn
+        ).then(
             fn=generate_build_audio,
             inputs=[],
-            outputs=[
-                build_audio_player,
-                build_audio_btn
-            ]
+            outputs=[build_audio_player, build_audio_btn],
+            show_progress="minimal"
+        ).then(
+            fn=lambda: gr.update(value="🔊 Listen to Portfolio", interactive=True),
+            outputs=build_audio_btn
         )
 
         # Compare/debate audio button
         compare_audio_btn.click(
+            fn=lambda: gr.update(value="Generating...", interactive=False),
+            outputs=compare_audio_btn
+        ).then(
             fn=generate_debate_audio,
             inputs=[],
-            outputs=[
-                compare_audio_player,
-                compare_audio_btn
-            ]
+            outputs=[compare_audio_player, compare_audio_btn],
+            show_progress="minimal"
+        ).then(
+            fn=lambda: gr.update(value="🎭 Listen to Debate", interactive=True),
+            outputs=compare_audio_btn
         )
 
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