Fix CORS documentation example to properly handle preflight requests

The previous example only allowed GET methods, causing browser preflight
requests to fail with "Disallowed CORS method" errors. Updated to include
the required parameters for proper CORS support with MCP clients.

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

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

CLAUDE.md

@@ -27,4 +27,9 @@ Only use HTTP transport when testing network-specific features. Prefer Streamabl
 # Only when network testing is required
 async with Client(transport=StreamableHttpTransport(server_url)) as client:
     result = await client.ping()
-```
+```
+
+## Development Workflow
+
+- You must always run pre-commit if you open a PR, because it is run as part of a required check.
+- When opening PRs, apply labels appropriately for bugs/breaking changes/enhancements/features. Generally, improvements are enhancements (not features) unless told otherwise.

docs/deployment/asgi.mdx

@@ -96,7 +96,13 @@ mcp = FastMCP("MyServer")
 
 # Define custom middleware
 custom_middleware = [
-    Middleware(CORSMiddleware, allow_origins=["*"]),
+    Middleware(
+        CORSMiddleware,
+        allow_origins=["https://example.com", "https://app.example.com"],
+        allow_credentials=True,
+        allow_methods=["GET", "POST", "OPTIONS"],
+        allow_headers=["Content-Type", "Authorization"],
+    ),
 ]
 
 # Create ASGI app with custom middleware