fix: allow MIME type parameters in resource validation (RFC 2045) (#1755)

Co-authored-by: Claude <noreply@anthropic.com>

src/mcp/server/fastmcp/resources/base.py

@@ -28,7 +28,7 @@ class Resource(BaseModel, abc.ABC):
     mime_type: str = Field(
         default="text/plain",
         description="MIME type of the resource content",
-        pattern=r"^[a-zA-Z0-9]+/[a-zA-Z0-9\-+.]+$",
+        pattern=r"^[a-zA-Z0-9]+/[a-zA-Z0-9\-+.]+(;\s*[a-zA-Z0-9\-_.]+=[a-zA-Z0-9\-_.]+)*$",
     )
     icons: list[Icon] | None = Field(default=None, description="Optional list of icons for this resource")
     annotations: Annotations | None = Field(default=None, description="Optional annotations for the resource")