feat(windows): Phase 6 C2 — close-to-tray + Settings toggle 持久化

- ui/settings-page.slint: SettingsToggleRow 的 toggled callback
  从 (bool) 改成 (string, bool) — 把 row 自己的 label + 新 value
  一起交给 caller；row 内部先 value=!value 再 emit；value 改
  in-out property 让内部可以 flip；SettingsPage 加 callback
  toggle-persist(string, bool)；7 个真 toggle 全部 wire 到
  toggle-persist（Notifications 4 + Startup 3）
- ui/app.slint: MainWindow 加 in-out property ×7 +
  setting-toggled(string, bool) callback；启动从 ActiveConfig
  装载；SettingsPage section 把 7 个 property forward 给 page +
  toggle-persist 转接到 root.setting-toggled
- src/lib.rs:
  · 启动从 ActiveConfig 读 7 个 toggle 设到 MainWindow
  · 新 on_setting_toggled 回调：load AppConfig → 按 label 改
    对应字段 → save_config；start_with_windows 额外调
    startup::set_enabled 写 HKCU Run（Phase 6 C1）
  · on_close_requested 看 close_to_tray：true 时
    window().hide() + KeepWindowShown；false 时保持原来的
    HideWindow 行为

避坑：
- Slint 1.x callback 不能直接用 label 区分，必须 caller 传
  string 参数；改造 (bool) → (string, bool)
- 设置 in-out property 让 row 内部能 flip value 然后 emit
  新值（caller 收到的就是 post-flip 值）
- close_to_tray 在 UI MainWindow 上是 in-out property，Rust
  端用 get_close_to_tray() 实时读，所以 toggle 立刻影响
  close_requested 行为（不需要重启）
- on_close_requested 内部读 get_close_to_tray 要 upgrade()
  MainWindow weak handle，捕获空时 fallback false（默认
  close 而不是 hide）

验证：cargo build / build --release 都 exit 0，0 warning
- cargo test: 15 passed; 0 failed
- debug   35.64 MB, subsystem = WINDOWS_CUI
- release  9.78 MB, subsystem = WINDOWS_GUI

src/lib.rs

@@ -96,6 +96,18 @@ pub fn run() -> error::AppResult<()> {
         state_rc.borrow().last_window_height.max(0) as f32,
     )));
 
+    // ── Phase 6 C2: load live AppConfig toggles into MainWindow ───
+    {
+        let cfg = config::ActiveConfig::load()?;
+        ui.set_desktop_notify(cfg.desktop_notifications);
+        ui.set_sound(cfg.sound);
+        ui.set_notify_high(cfg.notify_high);
+        ui.set_notify_max(cfg.notify_max);
+        ui.set_start_with_windows(cfg.start_with_windows);
+        ui.set_start_minimized(cfg.start_minimized);
+        ui.set_close_to_tray(cfg.close_to_tray);
+    }
+
     // ── Phase 3 C2 + 4 C2 + 5 C1: HTTP catch-up, then channel for WS ────
     let cfg = config::ActiveConfig::load()?;
     let shared_model: Rc<VecModel<MessageItem>>;
@@ -261,6 +273,61 @@ pub fn run() -> error::AppResult<()> {
         }
     });
 
+    // ── Phase 6 C2: every other SettingsPage toggle (notifications,
+    // startup) routes through one callback. We dispatch on the `label`
+    // string the UI hands us, persist into `config.json`, and for
+    // `start_with_windows` we also write HKCU Run (Phase 6 C1).
+    ui.on_setting_toggled(|label, value| {
+        // Phase 6 C2 also: AppConfig is mutated through a fresh load +
+        // save because the toggle handler is a `Fn` (no captured
+        // mutex); this keeps the persistence path side-effect-only and
+        // doesn't risk racing with the close-requested save below.
+        let mut cfg = match storage::load_config() {
+            c => c,
+        };
+        let label_str = label.to_string();
+        let label_ref: &str = &label_str;
+        match label_ref {
+            "desktop_notifications" => cfg.desktop_notifications = value,
+            "sound" => cfg.sound = value,
+            "notify_high" => cfg.notify_high = value,
+            "notify_max" => cfg.notify_max = value,
+            "start_minimized" => cfg.start_minimized = value,
+            "close_to_tray" => {
+                cfg.close_to_tray = value;
+                // Runtime-only: also flip the MainWindow property so
+                // the close-requested handler picks up the new value
+                // immediately without a restart. The Slint callback
+                // already set root.close-to-tray = value on the UI
+                // side; we just mirror it in `cfg` so save_config
+                // captures the same value.
+            }
+            "start_with_windows" => {
+                cfg.start_with_windows = value;
+                #[cfg(windows)]
+                {
+                    use crate::windows::startup;
+                    if !startup::set_enabled(value) {
+                        tracing::warn!("startup: HKCU Run write failed");
+                    }
+                }
+                #[cfg(not(windows))]
+                {
+                    tracing::debug!("startup: not on Windows, skipping HKCU");
+                }
+            }
+            _ => {
+                tracing::warn!(label = %label_str, "settings: unknown toggle label");
+                return;
+            }
+        }
+        if let Err(e) = storage::save_config(&cfg) {
+            tracing::warn!(error = %e, label = %label_str, "settings: save_config failed");
+        } else {
+            tracing::info!(label = %label_str, value, "settings: toggle persisted");
+        }
+    });
+
     // ── Phase 2 C3 callbacks ───────────────────────────────────────
     ui.on_about_clicked({
         let ui_handle = ui.as_weak();
@@ -272,13 +339,20 @@ pub fn run() -> error::AppResult<()> {
         }
     });
 
-    // ── Phase 2 C3 / 5 C2: save state on OS-close ─────────────────
-    // Captures the current window geometry, theme, and last_message_id
-    // (already updated by the WS drain closure).
+    // ── Phase 2 C3 / 5 C2 / 6 C2: save state on OS-close ──────────
+    // Phase 6 C2: when `close_to_tray` is true, hide the window and
+    // pretend to honor the close (return `KeepWindowShown`); otherwise
+    // let Slint proceed with its default behavior (which hides the
+    // window on Windows so the process keeps running until Quit).
     ui.window().on_close_requested({
         let state_for_save = state_rc.clone();
         let ui_handle = ui.as_weak();
         move || {
+            let close_to_tray = ui_handle
+                .upgrade()
+                .map(|u| u.get_close_to_tray())
+                .unwrap_or(false);
+
             if let Some(ui) = ui_handle.upgrade() {
                 let size = ui.window().size();
                 let mut s = state_for_save.borrow_mut();
@@ -297,6 +371,14 @@ pub fn run() -> error::AppResult<()> {
                     "saved state.json on close"
                 );
             }
+
+            if close_to_tray {
+                if let Some(ui) = ui_handle.upgrade() {
+                    let _ = ui.window().hide();
+                    tracing::info!("close: window hidden (close-to-tray)");
+                    return slint::CloseRequestResponse::KeepWindowShown;
+                }
+            }
             slint::CloseRequestResponse::HideWindow
         }
     });