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/config.py

@@ -566,7 +566,7 @@ DEFAULT_CONFIG = {
     
     # Text-to-speech configuration
     "tts": {
-        "provider": "edge",  # "edge" (free) | "elevenlabs" (premium) | "openai" | "minimax" | "mistral" | "neutts" (local)
+        "provider": "edge",  # "edge" (free) | "elevenlabs" (premium) | "openai" | "xai" | "minimax" | "mistral" | "neutts" (local)
         "edge": {
             "voice": "en-US-AriaNeural",
             # Popular: AriaNeural, JennyNeural, AndrewNeural, BrianNeural, SoniaNeural
@@ -580,6 +580,12 @@ DEFAULT_CONFIG = {
             "voice": "alloy",
             # Voices: alloy, echo, fable, onyx, nova, shimmer
         },
+        "xai": {
+            "voice_id": "eve",
+            "language": "en",
+            "sample_rate": 24000,
+            "bit_rate": 128000,
+        },
         "mistral": {
             "model": "voxtral-mini-tts-2603",
             "voice_id": "c69964a6-ab8b-4f8a-9465-ec0925096ec8",  # Paul - Neutral
@@ -836,6 +842,22 @@ OPTIONAL_ENV_VARS = {
         "category": "provider",
         "advanced": True,
     },
+    "XAI_API_KEY": {
+        "description": "xAI API key",
+        "prompt": "xAI API key",
+        "url": "https://console.x.ai/",
+        "password": True,
+        "category": "provider",
+        "advanced": True,
+    },
+    "XAI_BASE_URL": {
+        "description": "xAI base URL override",
+        "prompt": "xAI base URL (leave empty for default)",
+        "url": None,
+        "password": False,
+        "category": "provider",
+        "advanced": True,
+    },
     "GLM_API_KEY": {
         "description": "Z.AI / GLM API key (also recognized as ZAI_API_KEY / Z_AI_API_KEY)",
         "prompt": "Z.AI / GLM API key",