Merge commit from fork

* Auto-enable DNS rebinding protection for localhost servers

When a FastMCP server is created with host="127.0.0.1" or "localhost"
and no explicit transport_security is provided, automatically enable
DNS rebinding protection. Both 127.0.0.1 and localhost are allowed
as valid hosts/origins since clients may use either to connect.

* Add tests for auto DNS rebinding protection on localhost

Tests verify that:
- Protection auto-enables for host=127.0.0.1
- Protection auto-enables for host=localhost
- Both 127.0.0.1 and localhost are in allowed hosts/origins
- Protection does NOT auto-enable for other hosts (e.g., 0.0.0.0)
- Explicit transport_security settings are not overridden

* Add IPv6 localhost (::1) support for DNS rebinding protection

Extend auto-enable DNS rebinding protection to also cover IPv6
localhost. When host="::1", protection is now auto-enabled with
appropriate allowed hosts ([::1]:*) and origins (http://[::1]:*).

* Fix import ordering in test file

src/mcp/server/fastmcp/server.py

@@ -174,6 +174,14 @@ class FastMCP(Generic[LifespanResultT]):
         auth: AuthSettings | None = None,
         transport_security: TransportSecuritySettings | None = None,
     ):
+        # Auto-enable DNS rebinding protection for localhost (IPv4 and IPv6)
+        if transport_security is None and host in ("127.0.0.1", "localhost", "::1"):
+            transport_security = TransportSecuritySettings(
+                enable_dns_rebinding_protection=True,
+                allowed_hosts=["127.0.0.1:*", "localhost:*", "[::1]:*"],
+                allowed_origins=["http://127.0.0.1:*", "http://localhost:*", "http://[::1]:*"],
+            )
+
         self.settings = Settings(
             debug=debug,
             log_level=log_level,