fix(voice-clone): persist clone info in localStorage, auto-merge into project knobs, fix clone ID detection in CreateModal

- Move voice clone cache from module-level memory to localStorage
  so it survives page refresh and works across browser tabs
- VoiceAvatarPlaceholder now syncs clone result to localStorage
  immediately after creation (both design and clone paths)
- usePodcastProjectState auto-merges voice clone cache into project
  knobs when loading a project (fills gap for projects created
  before voice clone or when voice clone was created after)
- CreateModal now detects voice clone IDs by prefix (vc_*) not
  just by VOICE_CLONE_ID constant, fixing the mismatch where
  VoiceSelector passes the actual clone ID but CreateModal
  expected the placeholder ID
- AudioRegenerateModal is intentionally per-scene override and
  does not write back to knobs (by design)
- trends.py handler added for podcast topic trend analysis

frontend/src/components/PodcastMaker/CreateModal.tsx

@@ -319,13 +319,19 @@ export const CreateModal: React.FC<CreateModalProps> = ({ onCreate, open, defaul
     
     // Include selected voice in knobs
     // If voice clone is selected, include voice clone metadata
-    const isVoiceClone = selectedVoiceId === VOICE_CLONE_ID || knobs.custom_voice_id === selectedVoiceId;
+    // VoiceSelector may pass VOICE_CLONE_ID, the actual clone ID (vc_*), or a system voice ID
+    const selectedLooksLikeClone = selectedVoiceId?.startsWith("vc_") || selectedVoiceId === "MY_VOICE_CLONE";
+    const isVoiceClone = selectedVoiceId === VOICE_CLONE_ID || selectedLooksLikeClone || knobs.custom_voice_id === selectedVoiceId;
     
     let voiceSampleUrl: string | undefined;
     let voiceCloneEngine: string | undefined;
     let customVoiceId: string | undefined;
     
     if (isVoiceClone) {
+      // If VoiceSelector already gave us the real clone ID, use it as fallback
+      if (selectedLooksLikeClone && selectedVoiceId !== VOICE_CLONE_ID) {
+        customVoiceId = selectedVoiceId;
+      }
       try {
         const voiceCloneInfo = await getLatestVoiceClone();
         if (voiceCloneInfo?.success && voiceCloneInfo.custom_voice_id) {