feat(symptom): add Symptom @Model + start/end sheets + ongoing card

- Symptom @Model with severity 1-5 clamp, isOngoing, duration helpers
- SymptomStartSheet / SymptomEndSheet / OngoingSymptomsCard
- RecordSheet 加 .symptom kind 入口
- RootView 增加 'records' tab + ArchiveListView placeholder
- HomeView 顶部加 OngoingSymptomsCard
- ModelsSchemaTests: 2 个 Symptom 烟测(ongoing predicate + severity clamp)

Note: Symptom 是 CLAUDE.md §10 清单外的新功能,由产品负责人决定加入。
ArchiveListView 仍是 placeholder,真实 C1 实现按计划在 W4。

康康/Features/Archive/ArchiveListView.swift

@@ -0,0 +1,19 @@
+import SwiftUI
+
+struct ArchiveListView: View {
+    var body: some View {
+        VStack(spacing: 12) {
+            Spacer()
+            TjPlaceholder(label: "records · 记录列表\n（C1 尚未实现）")
+                .frame(width: 280, height: 180)
+            Text("记录")
+                .font(.tjH2())
+                .foregroundStyle(Tj.Palette.text2)
+            Spacer()
+        }
+        .frame(maxWidth: .infinity, maxHeight: .infinity)
+        .background(Tj.Palette.sand.ignoresSafeArea())
+    }
+}
+
+#Preview { ArchiveListView() }