chore: log disabled category fallback during finalize

Agent-Logs-Url: https://github.com/Rustmail/rustmail/sessions/7f12ccf8-887b-4e84-8b8f-9f4629b1f1a4

Co-authored-by: Akinator31 <99099121+Akinator31@users.noreply.github.com>

Author: Copilot

crates/rustmail/src/modules/categories.rs

@@ -214,7 +214,14 @@ pub async fn finalize_with_category(
                 let parent = cat.discord_category_id.parse::<u64>().ok();
                 (parent, Some(cat.id.clone()))
             }
-            Some(_) | None => (None, None),
+            Some(cat) => {
+                eprintln!(
+                    "Selected category {} is disabled; falling back to default inbox",
+                    cat.id
+                );
+                (None, None)
+            }
+            None => (None, None),
         }
     } else {
         (None, None)