Landing page: testimonials slider, how-it-works page, 25 TTS voices

- Add testimonial slider with 8 fake caller reviews
- Add how-it-works page with visual architecture diagram
- Expand voice pools: Inworld 25 voices (14M/11F), ElevenLabs 22 (14M/8F)
- Voice pools auto-switch when TTS provider changes
- Add cover art locally, update cache-busted image refs
- Add "More from Luke" footer links (MMG, prints, YouTube)
- Ad channel configurable in settings UI

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

backend/services/tts.py

@@ -577,7 +577,12 @@ async def generate_speech_inworld(text: str, voice_id: str) -> tuple[np.ndarray,
     import base64
     import librosa
 
-    voice = INWORLD_VOICES.get(voice_id, DEFAULT_INWORLD_VOICE)
+    # voice_id is now the Inworld voice name directly (e.g. "Edward")
+    # Fall back to legacy mapping if it's an ElevenLabs ID
+    if voice_id in INWORLD_VOICES:
+        voice = INWORLD_VOICES[voice_id]
+    else:
+        voice = voice_id
 
     api_key = settings.inworld_api_key
     if not api_key: