feat(db): in-app recovery screen with upgrade button when DB version is too new (#4575)

* feat(db): in-app recovery screen with upgrade button when DB version is too new

When the SQLite user_version is newer than the app supports (SCHEMA_VERSION),
Database::init() fails and previously dead-ended in a native Retry/Exit dialog
(Retry just fails again). The app now boots a dedicated recovery screen instead.

- Detect the recoverable "version too new" case and surface it via init_status
  (kind="db_version_too_new" + db_version/supported_version); force-show the main
  window and skip normal AppState boot (recovery commands need only AppHandle).
- The recovery screen first checks for an available update:
  - update available  -> "Upgrade app" runs the updater (download + install +
    restart) with a download progress bar.
  - no update (already latest) -> warns that the DB is too new even for the latest
    build (likely a third-party client), so upgrading cannot help.
- install_update_and_restart now emits `update-download-progress` events; new
  `check_app_update_available` command.
- i18n: en / ja / zh / zh-TW.

Verified: pnpm typecheck + format:check + test:unit (351) green; cross-model
review of Rust correctness and recovery-mode safety (no AppState panic).

* fix(db): pre-check too-new DB before schema writes; exit on close in recovery mode

Addresses review feedback on the too-new-DB recovery flow.

- P1: stored_user_version_exceeds_supported() is now checked BEFORE
  Database::init(), so create_tables()'s DDL (incl. the unconditional
  DROP INDEX/DROP TABLE IF EXISTS failover_queue) never runs against a
  database whose user_version we cannot understand. The earlier
  post-init-failure recovery branch is removed; the pre-check is the
  single authoritative guard, so "don't write to a DB we can't read"
  now holds from the very first DB access.

- P2: the window CloseRequested handler now detects recovery mode
  (init_error kind = db_version_too_new) and exits the app instead of
  honoring minimize_to_tray_on_close. Recovery mode returns before the
  tray is created, so hiding the window would leave the app running with
  no tray to bring it back; native-close now quits cleanly.

Verified: cargo fmt --check clean; cross-model Rust review of both fixes
(compile-correctness + no normal-startup/close regression).

src-tauri/src/commands/settings.rs

@@ -1,8 +1,15 @@
 #![allow(non_snake_case)]
 
-use tauri::AppHandle;
+use tauri::{AppHandle, Emitter};
 use tauri_plugin_updater::UpdaterExt;
 
+/// 应用更新下载进度（通过 `update-download-progress` 事件发给前端）。
+#[derive(Clone, serde::Serialize)]
+struct UpdateDownloadProgress {
+    downloaded: u64,
+    total: Option<u64>,
+}
+
 fn merge_settings_for_save(
     mut incoming: crate::settings::AppSettings,
     existing: &crate::settings::AppSettings,
@@ -203,8 +210,22 @@ pub async fn install_update_and_restart(app: AppHandle) -> Result<bool, String>
     };
 
     log::info!("开始下载应用更新: {}", update.version);
+    let progress_handle = app.clone();
+    let mut downloaded: u64 = 0;
     let bytes = update
-        .download(|_, _| {}, || {})
+        .download(
+            move |chunk_len, content_len| {
+                downloaded = downloaded.saturating_add(chunk_len as u64);
+                let _ = progress_handle.emit(
+                    "update-download-progress",
+                    UpdateDownloadProgress {
+                        downloaded,
+                        total: content_len,
+                    },
+                );
+            },
+            || {},
+        )
         .await
         .map_err(|e| format!("下载更新失败: {e}"))?;
 
@@ -245,6 +266,24 @@ pub async fn install_update_and_restart(app: AppHandle) -> Result<bool, String>
     }
 }
 
+/// 检查是否有可用的应用更新，返回可用的新版本号（无更新时返回 None）。
+///
+/// 数据库版本过新的恢复界面用它判断：升级应用能否解决问题。若返回 None，说明
+/// 已是最新版本，但数据库仍不兼容（通常由第三方客户端或更高版本创建），应提示用户
+/// 升级无法解决，而不是让其反复尝试。
+#[tauri::command]
+pub async fn check_app_update_available(app: AppHandle) -> Result<Option<String>, String> {
+    let updater = app
+        .updater_builder()
+        .build()
+        .map_err(|e| format!("初始化更新器失败: {e}"))?;
+    let update = updater
+        .check()
+        .await
+        .map_err(|e| format!("检查更新失败: {e}"))?;
+    Ok(update.map(|u| u.version))
+}
+
 /// 获取 app_config_dir 覆盖配置 (从 Store)
 #[tauri::command]
 pub async fn get_app_config_dir_override(app: AppHandle) -> Result<Option<String>, String> {