fix: resolve all Rust test compile warnings without suppression

Remove unused imports and a dead test helper, and strengthen tests that
held unused bindings/fields so the values are actually exercised:
- drop unused imports (HttpConfig, MediaType, std::io::Write)
- remove unused TestEventEmitter::clear helper
- replace meaningless size_of asserts with real empty-manager checks
- assert on MockTrack.name in sorting tests

src-tauri/src/commands/repository.rs

@@ -499,16 +499,16 @@ mod tests {
     #[test]
     fn test_repository_manager_creation() {
         let manager = RepositoryManager::new();
-        // Should be able to create RepositoryManager without panicking
-        assert_eq!(std::mem::size_of::<RepositoryManager>() > 0, true);
+        // A freshly created manager holds no repositories
+        assert!(manager.get("any-handle").is_none());
     }
 
     #[test]
     fn test_repository_manager_wrapper_structure() {
         let manager = RepositoryManager::new();
         let wrapper = RepositoryManagerWrapper(manager);
-        // Verify wrapper holds the manager
-        assert_eq!(std::mem::size_of::<RepositoryManagerWrapper>() > 0, true);
+        // The wrapper exposes the underlying manager, which starts empty
+        assert!(wrapper.0.get("any-handle").is_none());
     }
 
     #[test]