sync the docs with code

[minhsaco99]

Description

Update documentation to include TTS endpoints that were missing from README and API
docs.

Changes:

• Added TTS endpoints (/tts/synthesize, /tts/synthesize/stream) to README API
  overview table
• Added TTS usage examples (batch and streaming) to README
• Added deployment guide link to README documentation section
• Added full TTS endpoints documentation to docs/api.md with query parameters,
  examples, and JavaScript client code
• Added TTS data models (TTSResponse, TTSChunk, TTSPerformanceMetrics) to API
  docs

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• New Engine (STT/TTS provider)
• Breaking change (fix or feature that would cause existing functionality to not
  work as expected)
• Refactor (non-breaking code cleanup or optimization)
• Documentation update
• Performance improvement

Checklist

• I have read the CONTRIBUTING guide
• My code follows the project's code style (make format)
• Linting passes (make lint)
• Tests pass (make test)
• Documentation updated (if needed)
• No sensitive information (API keys, secrets) included

Related Issues

Closes #

Testing & Verification

Automated Tests

• Unit tests added/updated
• All existing tests pass

Manual Verification (if applicable)

• Verified markdown renders correctly
• Verified all links and code examples are accurate

API Endpoints Tested (if applicable)

N/A - Documentation only

Engine-Specific Tests (if applicable)

N/A

Security Impact

• No security implications
• Security impact (please describe below)

[minhsaco99]

@phonk2682