feat: update TypeScript SDK to implement draft spec changes for structured tool output

- Add outputSchema support to Tool interface with proper documentation
- Split CallToolResult into structured and unstructured variants
- Change structuredContent from string to object type
- Add validation that tools without outputSchema cannot return structuredContent
- Add validation that tools with outputSchema must return structuredContent
- Update client to validate structured content as object (no JSON parsing)
- Update tests to use object format for structuredContent
- Add tests for new validation constraints
- Update LATEST_PROTOCOL_VERSION to DRAFT-2025-v2

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/client/index.ts

@@ -438,11 +438,8 @@ export class Client<
       }
 
       try {
-        // Parse the structured content as JSON
-        const contentData = JSON.parse(result.structuredContent as string);
-        
-        // Validate the content against the schema
-        const validationResult = outputSchema.safeParse(contentData);
+        // Validate the structured content (which is already an object) against the schema
+        const validationResult = outputSchema.safeParse(result.structuredContent);
         
         if (!validationResult.success) {
           throw new McpError(
@@ -459,6 +456,14 @@ export class Client<
           `Failed to validate structured content: ${error instanceof Error ? error.message : String(error)}`
         );
       }
+    } else {
+      // If tool doesn't have outputSchema, it MUST NOT return structuredContent
+      if (result.structuredContent) {
+        throw new McpError(
+          ErrorCode.InvalidRequest,
+          `Tool without outputSchema cannot return structuredContent`
+        );
+      }
     }
 
     return result;