feat(tools): add Grok (xAI) as web_search provider

Add xAI's Grok as a new web_search provider alongside Brave and Perplexity.
Uses the xAI /v1/responses API with tools: [{type: "web_search"}].

Configuration:
- tools.web.search.provider: "grok"
- tools.web.search.grok.apiKey or XAI_API_KEY env var
- tools.web.search.grok.model (default: grok-4-1-fast)
- tools.web.search.grok.inlineCitations (optional, embeds markdown links)

Returns AI-synthesized answers with citations similar to Perplexity.

src/config/types.tools.ts

@@ -336,8 +336,8 @@ export type ToolsConfig = {
     search?: {
       /** Enable web search tool (default: true when API key is present). */
       enabled?: boolean;
-      /** Search provider ("brave" or "perplexity"). */
-      provider?: "brave" | "perplexity";
+      /** Search provider ("brave", "perplexity", or "grok"). */
+      provider?: "brave" | "perplexity" | "grok";
       /** Brave Search API key (optional; defaults to BRAVE_API_KEY env var). */
       apiKey?: string;
       /** Default search results count (1-10). */
@@ -355,6 +355,15 @@ export type ToolsConfig = {
         /** Model to use (defaults to "perplexity/sonar-pro"). */
         model?: string;
       };
+      /** Grok-specific configuration (used when provider="grok"). */
+      grok?: {
+        /** API key for xAI (defaults to XAI_API_KEY env var). */
+        apiKey?: string;
+        /** Model to use (defaults to "grok-4-1-fast"). */
+        model?: string;
+        /** Include inline citations in response text as markdown links (default: false). */
+        inlineCitations?: boolean;
+      };
     };
     fetch?: {
       /** Enable web fetch tool (default: true). */

src/config/zod-schema.agent-runtime.ts

@@ -171,7 +171,7 @@ export const ToolPolicySchema = ToolPolicyBaseSchema.superRefine((value, ctx) =>
 export const ToolsWebSearchSchema = z
   .object({
     enabled: z.boolean().optional(),
-    provider: z.union([z.literal("brave"), z.literal("perplexity")]).optional(),
+    provider: z.union([z.literal("brave"), z.literal("perplexity"), z.literal("grok")]).optional(),
     apiKey: z.string().optional(),
     maxResults: z.number().int().positive().optional(),
     timeoutSeconds: z.number().int().positive().optional(),
@@ -184,6 +184,14 @@ export const ToolsWebSearchSchema = z
       })
       .strict()
       .optional(),
+    grok: z
+      .object({
+        apiKey: z.string().optional(),
+        model: z.string().optional(),
+        inlineCitations: z.boolean().optional(),
+      })
+      .strict()
+      .optional(),
   })
   .strict()
   .optional();