feat(xai): upgrade to Responses API, add TTS provider

Cherry-picked and trimmed from PR #10600 by Jaaneek.

- Switch xAI transport from openai_chat to codex_responses (Responses API)
- Add codex_responses detection for xAI in all runtime_provider resolution paths
- Add xAI api_mode detection in AIAgent.__init__ (provider name + URL auto-detect)
- Add extra_headers passthrough for codex_responses requests
- Add x-grok-conv-id session header for xAI prompt caching
- Add xAI reasoning support (encrypted_content include, no effort param)
- Move x-grok-conv-id from chat_completions path to codex_responses path
- Add xAI TTS provider (dedicated /v1/tts endpoint with Opus conversion)
- Add xAI provider aliases (grok, x-ai, x.ai) across auth, models, providers, auxiliary
- Trim xAI model list to agentic models (grok-4.20-reasoning, grok-4-1-fast-reasoning)
- Add XAI_API_KEY/XAI_BASE_URL to OPTIONAL_ENV_VARS
- Add xAI TTS config section, setup wizard entry, tools_config provider option
- Add shared xai_http.py helper for User-Agent string

Co-authored-by: Jaaneek <Jaaneek@users.noreply.github.com>

hermes_cli/auth.py

@@ -928,6 +928,7 @@ def resolve_provider(
     _PROVIDER_ALIASES = {
         "glm": "zai", "z-ai": "zai", "z.ai": "zai", "zhipu": "zai",
         "google": "gemini", "google-gemini": "gemini", "google-ai-studio": "gemini",
+        "x-ai": "xai", "x.ai": "xai", "grok": "xai",
         "kimi": "kimi-coding", "kimi-for-coding": "kimi-coding", "moonshot": "kimi-coding",
         "kimi-cn": "kimi-coding-cn", "moonshot-cn": "kimi-coding-cn",
         "arcee-ai": "arcee", "arceeai": "arcee",