refactor: Remove deprecated ElevenLabs provider mapping

- Remove 'elevenlabs' fallback from providerVoiceField mapping
- ElevenLabs is no longer supported in AgentVibes
- Only Piper and macOS providers remain

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tools/cli/installers/lib/core/manifest-generator.js

@@ -618,7 +618,6 @@ class ManifestGenerator {
     // Map provider names to voice field names
     const providerVoiceField = {
       piper: 'piper',
-      elevenlabs: 'piper', // ElevenLabs not used, fallback to piper
       macos: 'mac',
     };