[codex] Fix MiniMax TTS fallback and HTML extraction

[dragon-hh]

Summary

This PR fixes two provider-integration issues found while running OpenMAIC with a server-configured MiniMax setup:

• allow server-configured TTS credentials to be reused when clients echo the provider's server base URL back to /api/generate/tts
• make interactive HTML extraction tolerant of truncated or unterminated fenced HTML responses from non-default LLM providers

Root cause

The TTS API previously treated any request-level ttsBaseUrl as a fully client-supplied provider configuration. When the UI sent the server-synced MiniMax serverBaseUrl, the route skipped the server API key fallback and failed with API key required for TTS provider: minimax-tts.

Interactive widget generation also required a complete </html> document or a closed Markdown code fence. Some model responses start with valid HTML inside a ```html block but may omit the final </html> or closing fence, causing scene-content generation to fail even though usable HTML was present.

Changes

• Normalize and compare requested TTS base URLs against the server-configured provider URL before deciding whether to require client credentials.
• Avoid passing server-only TTS base URLs from the settings preview path as client custom URLs.
• Export and harden extractHtml so valid started HTML can be extracted even when the model response is truncated.
• Add regression coverage for unterminated HTML code blocks.

Validation

pnpm test tests/generation/scene-generator-language-directive.test.ts tests/audio/minimax-tts-models.test.ts tests/server/provider-config.test.ts tests/store/settings-server-sync.test.ts

Result: 4 test files passed, 82 tests passed.