feat: block official provider switching during proxy takeover

Prevent users from switching to official providers (Anthropic/OpenAI/Google)
when proxy takeover is active, as using a proxy with official APIs may cause
account bans.

Defense-in-depth across 4 layers:
- Backend: ProviderService::switch(), hot_switch_provider(), switch_proxy_provider command
- Frontend: useProviderActions soft guard with error toast
- UI: ProviderActions button disabled with ShieldAlert icon
- Tray menu: official provider items disabled with ⛔ indicator

Also warns when enabling proxy takeover while current provider is official.

src-tauri/src/tray.rs

@@ -297,6 +297,9 @@ pub fn create_tray_menu(
             .map_err(|e| AppError::Message(format!("创建打开主界面菜单失败: {e}")))?;
     menu_builder = menu_builder.item(&show_main_item).separator();
 
+    // Pre-compute proxy running state (used to disable official providers in tray menu)
+    let is_proxy_running = futures::executor::block_on(app_state.proxy_service.is_running());
+
     // 每个应用类型折叠为子菜单，避免供应商过多时菜单过长
     for section in TRAY_SECTIONS.iter() {
         if !visible_apps.is_visible(&section.app_type) {
@@ -327,15 +330,32 @@ pub fn create_tray_menu(
             };
             let submenu_id = format!("submenu_{}", app_type_str);
 
+            // Check if this app is under proxy takeover (for disabling official providers)
+            let is_app_taken_over = is_proxy_running
+                && (futures::executor::block_on(app_state.db.get_live_backup(app_type_str))
+                    .ok()
+                    .flatten()
+                    .is_some()
+                    || app_state
+                        .proxy_service
+                        .detect_takeover_in_live_config_for_app(&section.app_type));
+
             let mut submenu_builder = SubmenuBuilder::with_id(app, &submenu_id, &submenu_label);
 
             for (id, provider) in sort_providers(&providers) {
                 let is_current = current_id == *id;
+                let is_official_blocked =
+                    is_app_taken_over && provider.category.as_deref() == Some("official");
+                let label = if is_official_blocked {
+                    format!("{} \u{26D4}", &provider.name) // ⛔ emoji
+                } else {
+                    provider.name.clone()
+                };
                 let item = CheckMenuItem::with_id(
                     app,
                     format!("{}{}", section.prefix, id),
-                    &provider.name,
-                    true,
+                    &label,
+                    !is_official_blocked, // disabled when blocked
                     is_current,
                     None::<&str>,
                 )