docs: clarify AIToolCall.name references snake_case convention from AIToolDefinition

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/spec/src/contracts/ai-service.ts

@@ -75,7 +75,7 @@ export interface AIToolDefinition {
 export interface AIToolCall {
     /** Unique ID for this tool call */
     id: string;
-    /** Tool name */
+    /** Tool name (must match an AIToolDefinition name, snake_case) */
     name: string;
     /** JSON-stringified arguments */
     arguments: string;