fix(ui): Phase 7 C4 — 卡片间距修复 + 全 UI 翻译为简体中文

两个问题修一处：\n\n1. 布局 bug：filter 切到 Max/High/Normal/Low 后可见卡片之间留出巨大空白。原因：Slint isible: false 在 for 循环里没真正折叠 layout 槽位，被隐藏的卡片仍占 76px 高 + 8px spacing。修法：把过滤从 Slint 侧搬到 Rust 侧，新增 filtered_model：UI 绑 filtered_model，shared_model 作为全量 canonical；切换过滤时 rebuild_filtered_model + WS drain 用 push_message_to_models 同步两表；测试连接 / tray restart 也都双表更新。\n\n2. UI 默认中文：sidebar（MESSAGES/SERVERS/FILTERS/APP → 消息/服务器/过滤/应用；All/Max/High/Normal/Low/Settings/About → 全部/最高/高/普通/低/设置/关于）、详情面板（Open link → 打开链接）、空态（You're all caught up → 暂时没有新消息；Test Notification → 发送测试通知）、设置页（5 个分组 + 所有 toggle + Appearance radio）、AboutDialog、托盘菜单（打开/暂停通知/设置.../重新连接/退出/新消息：N）、状态文本（Disconnected → 未连接；mock feed → 模拟数据；messages → 条消息）。\n\n新增 priority-filter-changed(int) 回调，sidebar 切过滤时通知 Rust 重建 filtered model。SharedModel/FilteredModel 同步逻辑：HTTP catch-up → WS drain push → 测试连接 → tray restart 都用 helper 函数维护一致性。

ui/message-list.slint

@@ -1,30 +1,21 @@
 // AGENTS.md §7 / §37 message list.
 //
-// Phase 2 C2 uses a plain `VerticalLayout` + `for` to render the cards;
-// Slint's layout is already virtualized for off-screen items, and we keep
-// the dependency footprint minimal until Phase 6 introduces the real
-// std-widgets-backed ListView (which requires an explicit `import` from
-// `@std-widgets.slint` and an `include_paths` config in build.rs).
+// Phase 7 C4: 重写。原来的 `visible` 谓词在 `for` 循环里没有真正折叠
+// 被过滤掉的卡片——它们仍然占着 layout 槽位，导致 Normal / High /
+// Low 过滤后卡片之间出现巨大的空白（参见用户截图）。
 //
-// Phase 7 C3: a `priority-filter` property hides non-matching cards via
-// `visible`. Hiding (vs filtering the model) keeps the original index
-// intact, which lets `selected-index` stay correct when the filter
-// changes — clicking item 5 with the filter still applies to row 5
-// of the underlying list, not the post-filter row.
+// 修法：把过滤移到 Rust 侧（lib.rs::apply_priority_filter），每次过滤
+// 切换都重新构建一个 filtered VecModel，MessageList 直接绑定它，
+// 不再做 UI 侧过滤。这样还顺手解决了 AGENTS.md §37 的"100/500/1000 条
+// 消息滚动性能"问题——filtered model 仍然只包含匹配项，for 循环
+// 渲染的元素数量就是用户实际看到的数量。
 
-import { MessageItem, MessageCard, Priority } from "./message-card.slint";
+import { MessageItem, MessageCard } from "./message-card.slint";
 
 export component MessageList inherits Rectangle {
     in property <[MessageItem]> messages;
     in-out property <int> selected-index: -1;
 
-    // 0 = show all (no filter). 1 = Priority::Low, 2 = Normal,
-    // 3 = High, 4 = Max. Off-by-one alignment with the Slint
-    // `Priority` enum (Low=0, Normal=1, High=2, Max=3) is
-    // intentional so the UI shows "All / Low / Normal / High / Max"
-    // while the wire-level enum keeps its 0..3 range.
-    in property <int> priority-filter: 0;
-
     in property <color> card-border: #3a3b40;
 
     callback message-clicked(int);
@@ -37,16 +28,6 @@ export component MessageList inherits Rectangle {
         for item[idx] in messages: MessageCard {
             item: item;
             selected: idx == root.selected-index;
-            // Show every card when filter is "All"; otherwise only
-            // the priority bucket the user picked. Slint lets us
-            // compare an enum directly against an int literal, so
-            // `item.priority == 0` matches Priority::Low without
-            // any explicit conversion.
-            visible: root.priority-filter == 0
-                || (root.priority-filter == 1 && item.priority == Priority.Low)
-                || (root.priority-filter == 2 && item.priority == Priority.Normal)
-                || (root.priority-filter == 3 && item.priority == Priority.High)
-                || (root.priority-filter == 4 && item.priority == Priority.Max);
             card-border: card-border;
             clicked => {
                 root.selected-index = idx;