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/tools_config.py

@@ -146,6 +146,14 @@ TOOL_CATEGORIES = {
                 ],
                 "tts_provider": "openai",
             },
+            {
+                "name": "xAI TTS",
+                "tag": "Grok voices - requires xAI API key",
+                "env_vars": [
+                    {"key": "XAI_API_KEY", "prompt": "xAI API key", "url": "https://console.x.ai/"},
+                ],
+                "tts_provider": "xai",
+            },
             {
                 "name": "ElevenLabs",
                 "badge": "paid",