fix: append /mcp to resource_server_url with trailing slash handling

Append '/mcp' to resource_server_url and handle trailing slashes to ensure
proper OAuth Protected Resource Metadata validation. This prevents the error:
"Protected Resource Metadata resource does not match MCP server resolved resource"
which occurs when the PRM resource URL doesn't exactly match the server URL.

Fixes compatibility with VS Code + MCP authentication per RFC 9728.

References: microsoft/vscode#255255

Author: shulkx

examples/servers/simple-auth/mcp_simple_auth/server.py

@@ -79,7 +79,7 @@ def create_resource_server(settings: ResourceServerSettings) -> FastMCP:
         auth=AuthSettings(
             issuer_url=settings.auth_server_url,
             required_scopes=[settings.mcp_scope],
-            resource_server_url=settings.server_url,
+            resource_server_url=AnyHttpUrl(f"{str(settings.server_url).rstrip('/')}/mcp"),
         ),
     )