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/Features/Symptom/SymptomEndSheet.swift

@@ -104,16 +104,3 @@ struct SymptomEndSheet: View {
     }
 }
 
-func formatDuration(_ interval: TimeInterval) -> String {
-    let totalMinutes = Int(interval / 60)
-    let days = totalMinutes / (60 * 24)
-    let hours = (totalMinutes % (60 * 24)) / 60
-    let minutes = totalMinutes % 60
-
-    if days > 0 && hours > 0 { return "\(days) 天 \(hours) 小时" }
-    if days > 0 { return "\(days) 天" }
-    if hours > 0 && minutes > 0 { return "\(hours) 小时 \(minutes) 分" }
-    if hours > 0 { return "\(hours) 小时" }
-    if minutes > 0 { return "\(minutes) 分钟" }
-    return "刚刚"
-}