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/Diary/DiaryQuickSheet.swift

@@ -0,0 +1,102 @@
+import SwiftUI
+import SwiftData
+
+struct DiaryQuickSheet: View {
+    @Environment(\.modelContext) private var ctx
+    @Environment(\.dismiss) private var dismiss
+
+    @State private var content: String = ""
+    @State private var createdAt: Date = .now
+
+    private var canSubmit: Bool {
+        !content.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
+    }
+
+    var body: some View {
+        VStack(spacing: 0) {
+            Capsule()
+                .fill(Tj.Palette.line)
+                .frame(width: 40, height: 4)
+                .padding(.top, 10)
+                .padding(.bottom, 14)
+
+            HStack {
+                Text("写日记")
+                    .font(.tjH2())
+                    .foregroundStyle(Tj.Palette.text)
+                Spacer()
+                Text("本机保存")
+                    .font(.system(size: 12))
+                    .foregroundStyle(Tj.Palette.text3)
+            }
+            .padding(.horizontal, 20)
+            .padding(.bottom, 16)
+
+            VStack(alignment: .leading, spacing: 16) {
+                VStack(alignment: .leading, spacing: 8) {
+                    sectionLabel("内容")
+                    TextField("今天怎么样?", text: $content, axis: .vertical)
+                        .lineLimit(4...10)
+                        .padding(.horizontal, 14)
+                        .padding(.vertical, 12)
+                        .background(
+                            RoundedRectangle(cornerRadius: Tj.Radius.sm, style: .continuous)
+                                .fill(Tj.Palette.paper)
+                        )
+                        .overlay(
+                            RoundedRectangle(cornerRadius: Tj.Radius.sm, style: .continuous)
+                                .strokeBorder(Tj.Palette.line, lineWidth: 1)
+                        )
+                }
+
+                VStack(alignment: .leading, spacing: 8) {
+                    sectionLabel("时间")
+                    DatePicker("", selection: $createdAt, in: ...Date.now)
+                        .datePickerStyle(.compact)
+                        .labelsHidden()
+                }
+            }
+            .padding(.horizontal, 20)
+
+            Spacer(minLength: 12)
+
+            HStack(spacing: 12) {
+                Button("取消") { dismiss() }
+                    .buttonStyle(TjGhostButton(height: 44, fontSize: 15, horizontalPadding: 18))
+                Button("保存") { submit() }
+                    .buttonStyle(TjPrimaryButton(height: 44, fontSize: 15, horizontalPadding: 18))
+                    .disabled(!canSubmit)
+                    .opacity(canSubmit ? 1 : 0.4)
+            }
+            .padding(.horizontal, 20)
+            .padding(.vertical, 14)
+        }
+        .background(
+            Tj.Palette.sand
+                .clipShape(RoundedRectangle(cornerRadius: Tj.Radius.xl, style: .continuous))
+                .ignoresSafeArea(edges: .bottom)
+        )
+        .presentationDetents([.medium, .large])
+        .presentationDragIndicator(.hidden)
+        .presentationBackground(Tj.Palette.sand)
+        .presentationCornerRadius(Tj.Radius.xl)
+    }
+
+    private func sectionLabel(_ text: String) -> some View {
+        Text(text)
+            .font(.system(size: 12, weight: .semibold))
+            .tracking(0.3)
+            .foregroundStyle(Tj.Palette.text2)
+    }
+
+    private func submit() {
+        guard canSubmit else { return }
+        let entry = DiaryEntry(
+            content: content.trimmingCharacters(in: .whitespacesAndNewlines),
+            createdAt: createdAt
+        )
+        ctx.insert(entry)
+        try? ctx.save()
+        dismiss()
+    }
+}