fix: resolve clippy warnings and rustfmt issues for CI compliance

Fix all clippy lints (collapsible if, clone on Copy, needless borrow,
redundant bindings, unused params) and apply rustfmt across the codebase.
Update test mocks to match Uuid-based trait signatures.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/interfaces/api/handlers/caldav_handler.rs

@@ -299,13 +299,12 @@ async fn handle_propfind(
             } else {
                 // Not a calendar ID — treat as user calendar home (e.g. /caldav/{username}/)
                 // List all calendars for this user
-                let calendars =
-                    calendar_service
-                        .list_my_calendars(user.id)
-                        .await
-                        .map_err(|e| {
-                            AppError::internal_error(format!("Failed to list calendars: {}", e))
-                        })?;
+                let calendars = calendar_service
+                    .list_my_calendars(user.id)
+                    .await
+                    .map_err(|e| {
+                        AppError::internal_error(format!("Failed to list calendars: {}", e))
+                    })?;
 
                 let base_href = &format!("/caldav/{}/", first_segment);
                 let mut response_body = Vec::new();