feat: Update VoiceAssignmentSection to trigger script generation

- Changed 'Generate Audiobook' button to 'Next: Review Script'
- Added 'Skip Review & Generate' button as alternative
- Updated button handlers to call handleGenerateScript and handleSkipReview
- Updated button styling: primary button now blue for review, green for skip
- Maintains backward compatibility with optional onSkipReview prop

Requirements: 15.1, 15.8

frontend/src/App.tsx

@@ -195,6 +195,7 @@ function App() {
               speed={speed}
               onSpeedChange={handleSpeedChange}
               onGenerate={handleGenerateScript}
+              onSkipReview={handleSkipReview}
               isGenerating={isGeneratingScript}
               allRolesAssigned={allRolesAssigned}
             />