feat(timeline): TimelineRow + DateSection + grouping tests + Diary sheet

- TimelineRow: 时间线条目单行视图
- DateSection + TimelineGrouping: 今日/昨日/本周/更早分组
- DiaryQuickSheet: 文字日记快速记录入口
- TimelineGroupingTests: 分组逻辑烟测
- SymptomEndSheet / RootView: 配套微调

康康/RootView.swift

@@ -30,6 +30,7 @@ struct RootView: View {
     @State private var showRecordSheet = false
     @State private var activeFlow: ActiveFlow?
     @State private var showSymptomStart = false
+    @State private var showDiary = false
 
     var body: some View {
         VStack(spacing: 0) {
@@ -56,7 +57,7 @@ struct RootView: View {
                     case .quick:   activeFlow = .quick
                     case .archive: activeFlow = .archive
                     case .symptom: showSymptomStart = true
-                    case .diary:   break
+                    case .diary:   showDiary = true
                     }
                 }
             }
@@ -64,6 +65,9 @@ struct RootView: View {
         .sheet(isPresented: $showSymptomStart) {
             SymptomStartSheet()
         }
+        .sheet(isPresented: $showDiary) {
+            DiaryQuickSheet()
+        }
 #if os(iOS)
         .fullScreenCover(item: $activeFlow) { flow in
             switch flow {