fix(tools): strip xAI-unsupported JSON Schema keywords from tool definitions

xAI rejects minLength, maxLength, minItems, maxItems, minContains, and
maxContains in tool schemas with a 502 error instead of ignoring them.
This causes all requests to fail when any tool definition includes these
validation-constraint keywords (e.g. sessions_spawn uses maxLength and
maxItems on its attachment fields).

Add stripXaiUnsupportedKeywords() in schema/clean-for-xai.ts, mirroring
the existing cleanSchemaForGemini() pattern. Apply it in normalizeToolParameters()
when the provider is xai directly, or openrouter with an x-ai/* model id.

Fixes tool calls for x-ai/grok-* models both direct and via OpenRouter.

src/agents/pi-tools.ts

@@ -524,7 +524,10 @@ export function createOpenClawCodingTools(options?: {
   // Without this, some providers (notably OpenAI) will reject root-level union schemas.
   // Provider-specific cleaning: Gemini needs constraint keywords stripped, but Anthropic expects them.
   const normalized = subagentFiltered.map((tool) =>
-    normalizeToolParameters(tool, { modelProvider: options?.modelProvider }),
+    normalizeToolParameters(tool, {
+      modelProvider: options?.modelProvider,
+      modelId: options?.modelId,
+    }),
   );
   const withHooks = normalized.map((tool) =>
     wrapToolWithBeforeToolCallHook(tool, {