refactor(drive): match DriveKind directly instead of Drive::is_personal()

Drops the boolean is_personal() wrapper in favor of matching
DriveKind::Personal/Shared at the two call sites, matching the
exhaustive-match convention already used for DriveKind elsewhere
(as_str, parse, DriveKindDto::from).

src/domain/entities/drive.rs

@@ -131,12 +131,6 @@ impl Drive {
         self.default_for_user == Some(user_id)
     }
 
-    /// `true` if this drive is a personal drive of any kind (default or
-    /// secondary). Encapsulates the kind check at the call site.
-    pub fn is_personal(&self) -> bool {
-        matches!(self.kind, DriveKind::Personal)
-    }
-
     /// Typed view of `policies` for enforcement code. Lenient deserialise:
     /// unknown keys are preserved on disk (the column stays the canonical
     /// JSONB bag) but ignored here, missing keys default to `false`.