feat(markdown) remove id check & extraction

backend/markdown/src/error.rs

@@ -2,12 +2,6 @@ use thiserror::Error;
 
 #[derive(Error, Debug)]
 pub enum Error {
-    #[error("missing front-matter field: id")]
-    MissingID,
-
-    #[error("invalid file id: {}", msg)]
-    InvalidID { msg: String },
-
     #[error("invalid front-matter: {}", msg)]
     InvalidFrontMatter { msg: String },