fix: resolve test failures and clippy warnings

- tests/App.test.tsx: remove outdated SettingsPage mock, use dynamic import
- database/tests.rs: remove unused field, use struct init syntax
- deeplink/tests.rs: use idiomatic assert!() instead of assert_eq!(true)
- support.rs: add #[allow(dead_code)] for test utilities
- usage_stats.rs: code formatting

src-tauri/src/services/usage_stats.rs

@@ -255,8 +255,7 @@ impl Database {
             Ok(stats)
         } else {
             let today = Local::now().date_naive();
-            let start_day =
-                today - Duration::days((days.saturating_sub(1)) as i64);
+            let start_day = today - Duration::days((days.saturating_sub(1)) as i64);
             let start_of_window = start_day.and_hms_opt(0, 0, 0).unwrap();
             // 使用 earliest() 处理 DST 切换时的歧义时间，fallback 到当前时间减 days 天
             let start_ts = Local