feat(xai): add xAI Grok provider with OAuth + API key auth + image

Adapted from PR #1286 (mugnimaestra/feat/xai-grok-provider) to match
existing app architecture. Includes:

- OAuth 2.0 with PKCE on loopback port 56121 (Grok Build)
- API key auth path (console.x.ai)
- Token refresh wiring (open-sse + sse tokenRefresh)
- Dashboard OAuth modal with fixed-port flow + manual code fallback
- Provider registry entries (OAuth + API key)
- xAI image generation via OpenAI-compatible adapter
  (grok-2-image-1212 model, no size/quality/style params)

Excludes (intentionally, to match app patterns):
- Custom xAI Responses executor (DefaultExecutor handles /chat/completions)
- xAI-specific translators (app uses OpenAI as intermediate format)
- Image edits (not supported by current imageGenerationCore)
- Video endpoints (app has no video subsystem yet)
- CLI xai-login command

Refs decolua#1286

Co-authored-by: Cursor <cursoragent@cursor.com>

src/shared/constants/providers.js

@@ -60,6 +60,7 @@ export const OAUTH_PROVIDERS = {
   codex: { id: "codex", alias: "cx", name: "OpenAI Codex", icon: "code", color: "#3B82F6", deprecated: true, deprecationNotice: RISK_NOTICE, thinkingConfig: THINKING_CONFIG.effort, serviceKinds: ["llm", "image"], kindNotice: { image: "Requires a ChatGPT Plus (or higher) account. Free accounts are not supported for image generation." }, website: "https://chatgpt.com/codex", notice: { signupUrl: "https://chatgpt.com/codex" } },
   github: { id: "github", alias: "gh", name: "GitHub Copilot", icon: "code", color: "#333333", deprecated: true, deprecationNotice: RISK_NOTICE, serviceKinds: ["llm", "embedding"], embeddingConfig: { baseUrl: "https://models.github.ai/inference/embeddings", authType: "apikey", authHeader: "bearer", models: [{ id: "text-embedding-3-small", name: "Text Embedding 3 Small (GitHub)", dimensions: 1536 }, { id: "text-embedding-3-large", name: "Text Embedding 3 Large (GitHub)", dimensions: 3072 }] }, website: "https://github.com/features/copilot", notice: { signupUrl: "https://github.com/features/copilot" } },
   cursor: { id: "cursor", alias: "cu", name: "Cursor IDE", icon: "edit_note", color: "#00D4AA", website: "https://cursor.com", notice: { signupUrl: "https://cursor.com" } },
+  xai: { id: "xai", alias: "xai", name: "xAI (Grok)", icon: "auto_awesome", color: "#1DA1F2", textIcon: "XA", website: "https://x.ai", notice: { apiKeyUrl: "https://console.x.ai", signupUrl: "https://x.ai" }, serviceKinds: ["llm", "imageToText", "webSearch", "image"], searchViaChat: { defaultModel: "grok-4.20-reasoning", pricingUrl: "https://x.ai/api#pricing" }, authModes: ["oauth", "apikey"], hasOAuth: true },
   // "kimi-coding": { id: "kimi-coding", alias: "kmc", name: "Kimi Coding", icon: "psychology", color: "#1E40AF", textIcon: "KC" },
   kilocode: { id: "kilocode", alias: "kc", name: "Kilo Code", icon: "code", color: "#FF6B35", textIcon: "KC", website: "https://kilocode.ai", notice: { signupUrl: "https://kilocode.ai" } },
   cline: { id: "cline", alias: "cl", name: "Cline", icon: "smart_toy", color: "#5B9BD5", textIcon: "CL", website: "https://cline.bot", notice: { signupUrl: "https://cline.bot" } },
@@ -86,7 +87,7 @@ export const APIKEY_PROVIDERS = {
   deepseek: { id: "deepseek", alias: "ds", name: "DeepSeek", icon: "bolt", color: "#4D6BFE", textIcon: "DS", website: "https://deepseek.com", notice: { apiKeyUrl: "https://platform.deepseek.com/api_keys" } },
   commandcode: { id: "commandcode", alias: "cmc", name: "Command Code", icon: "smart_toy", color: "#000000", textIcon: "CC", website: "https://commandcode.ai", notice: { text: "Use your CommandCode CLI API key (starts with user_...) from ~/.commandcode/auth.json or commandcode.ai/studio.", apiKeyUrl: "https://commandcode.ai/studio" } },
   groq: { id: "groq", alias: "groq", name: "Groq", icon: "speed", color: "#F55036", textIcon: "GQ", website: "https://groq.com", notice: { apiKeyUrl: "https://console.groq.com/keys" }, serviceKinds: ["llm", "imageToText", "stt"], sttConfig: { baseUrl: "https://api.groq.com/openai/v1/audio/transcriptions", authType: "apikey", authHeader: "bearer", format: "openai", models: [{ id: "whisper-large-v3", name: "Whisper Large v3" }, { id: "whisper-large-v3-turbo", name: "Whisper Large v3 Turbo" }, { id: "distil-whisper-large-v3-en", name: "Distil Whisper Large v3 EN" }] } },
-  xai: { id: "xai", alias: "xai", name: "xAI (Grok)", icon: "auto_awesome", color: "#1DA1F2", textIcon: "XA", website: "https://x.ai", notice: { apiKeyUrl: "https://console.x.ai" }, serviceKinds: ["llm", "imageToText", "webSearch"], searchViaChat: { defaultModel: "grok-4.20-reasoning", pricingUrl: "https://x.ai/api#pricing" } },
+  xai: { id: "xai", alias: "xai", name: "xAI (Grok)", icon: "auto_awesome", color: "#1DA1F2", textIcon: "XA", website: "https://x.ai", notice: { apiKeyUrl: "https://console.x.ai" }, serviceKinds: ["llm", "imageToText", "webSearch", "image"], searchViaChat: { defaultModel: "grok-4.20-reasoning", pricingUrl: "https://x.ai/api#pricing" }, authModes: ["oauth", "apikey"], hasOAuth: true },
   mistral: { id: "mistral", alias: "mistral", name: "Mistral", icon: "air", color: "#FF7000", textIcon: "MI", website: "https://mistral.ai", notice: { apiKeyUrl: "https://console.mistral.ai/api-keys" }, serviceKinds: ["llm", "imageToText", "embedding"], embeddingConfig: { baseUrl: "https://api.mistral.ai/v1/embeddings", authType: "apikey", authHeader: "bearer", models: [{ id: "mistral-embed", name: "Mistral Embed", dimensions: 1024 }] } },
   perplexity: { id: "perplexity", alias: "pplx", name: "Perplexity", icon: "search", color: "#20808D", textIcon: "PP", website: "https://www.perplexity.ai", notice: { apiKeyUrl: "https://www.perplexity.ai/settings/api" }, serviceKinds: ["llm", "webSearch"], searchConfig: { baseUrl: "https://api.perplexity.ai/search", method: "POST", authType: "apikey", authHeader: "bearer", costPerQuery: 0.005, freeMonthlyQuota: 0, searchTypes: ["web"], defaultMaxResults: 5, maxMaxResults: 20, timeoutMs: 10000, cacheTTLMs: 300000 } },
   together: { id: "together", alias: "together", name: "Together AI", icon: "group_work", color: "#0F6FFF", textIcon: "TG", website: "https://www.together.ai", notice: { apiKeyUrl: "https://api.together.xyz/settings/api-keys" }, serviceKinds: ["llm", "embedding"], embeddingConfig: { baseUrl: "https://api.together.xyz/v1/embeddings", authType: "apikey", authHeader: "bearer", models: [{ id: "BAAI/bge-large-en-v1.5", name: "BGE Large EN v1.5", dimensions: 1024 }, { id: "togethercomputer/m2-bert-80M-8k-retrieval", name: "M2 BERT 80M 8K", dimensions: 768 }] } },