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/Timeline/DateSection.swift

@@ -0,0 +1,74 @@
+import Foundation
+
+enum DateSection: Hashable {
+    case today
+    case yesterday
+    case thisWeek
+    case thisMonth
+    case year(Int)
+
+    var label: String {
+        switch self {
+        case .today:        return "今天"
+        case .yesterday:    return "昨天"
+        case .thisWeek:     return "本周"
+        case .thisMonth:    return "本月"
+        case .year(let y):  return "\(y) 年"
+        }
+    }
+
+    var sortIndex: Int {
+        switch self {
+        case .today:       return 0
+        case .yesterday:   return 1
+        case .thisWeek:    return 2
+        case .thisMonth:   return 3
+        case .year(let y): return 10_000 - y
+        }
+    }
+}
+
+enum TimelineGrouping {
+    static func section(for date: Date,
+                        now: Date = .now,
+                        calendar: Calendar = .current) -> DateSection {
+        if calendar.isDateInToday(date) { return .today }
+        if calendar.isDateInYesterday(date) { return .yesterday }
+        if calendar.isDate(date, equalTo: now, toGranularity: .weekOfYear) {
+            return .thisWeek
+        }
+        if calendar.isDate(date, equalTo: now, toGranularity: .month) {
+            return .thisMonth
+        }
+        let year = calendar.component(.year, from: date)
+        return .year(year)
+    }
+
+    static func group(_ entries: [TimelineEntry],
+                      now: Date = .now,
+                      calendar: Calendar = .current)
+    -> [(section: DateSection, items: [TimelineEntry])] {
+        var buckets: [DateSection: [TimelineEntry]] = [:]
+        for entry in entries {
+            let key = section(for: entry.date, now: now, calendar: calendar)
+            buckets[key, default: []].append(entry)
+        }
+        return buckets
+            .map { ($0.key, $0.value.sorted { $0.date > $1.date }) }
+            .sorted { $0.0.sortIndex < $1.0.sortIndex }
+    }
+}
+
+func formatDuration(_ interval: TimeInterval) -> String {
+    let totalMinutes = Int(max(0, 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"
+}