feat(broadcast): add new app for ElevenLabs TTS audio generation

[chasepoirier]

Summary

This PR introduces the Broadcast app, a new Contentful Sidebar App that integrates with ElevenLabs Neural Text-to-Speech API to convert entry text into audio assets.

Features

• Secure API Integration: ElevenLabs API key stored as a secret installation parameter, only accessible in backend functions
• Voice Selection: Fetches available voices from ElevenLabs and presents them in a dropdown
• Field Selection: Supports Symbol, Text, and RichText field types for audio conversion
• Asset Management: Automatically creates and processes audio assets in Contentful
• Error Handling: User-friendly error messages for API errors, quota limits, and configuration issues

Architecture

• Frontend: React + TypeScript + Forma 36 components
• Backend: Contentful Functions for secure API calls
• Communication: App Actions for frontend-to-backend RPC

Files Added

Path	Purpose
contentful-app-manifest.json	Functions, actions, and network allowlist
functions/common.ts	Shared CMA client and types
functions/getVoices.ts	Fetches ElevenLabs voices
functions/generateAudio.ts	TTS generation and asset upload
src/locations/ConfigScreen.tsx	API key input and content type selector
src/locations/Sidebar.tsx	Voice selector, field selector, generate button

Testing

• TypeScript compilation passes
• Vite build succeeds
• Functions build succeeds

Next Steps

• Add unit tests for functions and components
• Create README.md with setup instructions
• End-to-end testing in a Contentful environment