feat(phase-4): UI/UX improvements for Podcast Maker Write phase

Frontend Changes:
- Add scene numbering badge (1/N) next to scene titles
- Add inline status chips (Complete, Audio, Image, Voice, Why Script)
- Professional AI-like gradient styling for all chips with shadows
- Remove Script Editor header and 'Why This Script Format?' collapsible
- Move Voice and Why Script info to per-scene chips
- Make scene section mobile-responsive (responsive layout, button sizing)
- Rename 'B-Roll Charts' to 'Podcast Charts' with accordion (collapsed by default)
- Add sceneIndex prop to SceneEditor for scene numbering
- Enhanced accessibility with keyboard navigation and focus states

Backend Changes:
- Audio handler improvements
- B-roll handler enhancements
- Script handler updates
- B-roll composer and service improvements
- Removed temporary broll_temp files

Technical:
- Full mobile responsiveness for scene cards
- Gradient chip styling: vibrant colors with white text and shadows
- Non-breaking approval/generation flow preserved
- TypeScript compatibility maintained

frontend/src/hooks/usePodcastProjectState.ts

@@ -70,6 +70,9 @@ const DEFAULT_KNOBS: Knobs = {
   voice_speed: 1,
   voice_id: "Wise_Woman",
   custom_voice_id: undefined,
+  is_voice_clone: undefined,
+  voice_sample_url: undefined,
+  voice_clone_engine: undefined,
   resolution: "720p",
   scene_length_target: 45,
   sample_rate: 24000,
@@ -443,7 +446,7 @@ export const usePodcastProjectState = () => {
         scriptData: dbProject.script_data,
         bible: dbProject.bible,
         renderJobs: dbProject.render_jobs || [],
-        knobs: dbProject.knobs || DEFAULT_KNOBS,
+        knobs: { ...DEFAULT_KNOBS, ...(dbProject.knobs || {}) },
         researchProvider: dbProject.research_provider || 'exa',
         budgetCap: dbProject.budget_cap || 50,
         showScriptEditor: dbProject.show_script_editor || false,