chore: unify code formatting and remove unused code

- Apply cargo fmt to Rust code with multiline error handling
- Apply Prettier formatting to TypeScript code with trailing commas
- Unify #[allow(non_snake_case)] attribute formatting
- Remove unused ProviderNotFound error variant from error.rs
- Add vitest-report.json to .gitignore to exclude test artifacts
- Optimize readability of error handling chains with vertical alignment

All tests passing: 22 Rust tests + 126 frontend tests

src-tauri/tests/provider_service.rs

@@ -240,8 +240,8 @@ fn provider_service_switch_missing_provider_returns_error() {
     let err = ProviderService::switch(&state, AppType::Claude, "missing")
         .expect_err("switching missing provider should fail");
     match err {
-        AppError::ProviderNotFound(id) => assert_eq!(id, "missing"),
-        other => panic!("expected ProviderNotFound, got {other:?}"),
+        AppError::Localized { key, .. } => assert_eq!(key, "provider.not_found"),
+        other => panic!("expected Localized error for provider not found, got {other:?}"),
     }
 }