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/Record/RecordSheet.swift

@@ -1,7 +1,7 @@
 import SwiftUI
 
 enum RecordKind: String, Identifiable, CaseIterable {
-    case quick, archive, diary
+    case quick, archive, diary, symptom
     var id: String { rawValue }
 
     var title: String {
@@ -9,13 +9,15 @@ enum RecordKind: String, Identifiable, CaseIterable {
         case .quick:   return "异常项快拍"
         case .archive: return "关键报告归档"
         case .diary:   return "文字日记"
+        case .symptom: return "症状开始"
         }
     }
     var subtitle: String {
         switch self {
         case .quick:   return "只记录单个或几项异常指标"
         case .archive: return "完整保存整份报告（可多页）"
-        case .diary:   return "记录症状、心情、用药"
+        case .diary:   return "记录心情、用药、其他"
+        case .symptom: return "开始一个持续症状，结束时再点结束"
         }
     }
     var icon: String {
@@ -23,6 +25,7 @@ enum RecordKind: String, Identifiable, CaseIterable {
         case .quick:   return "camera.fill"
         case .archive: return "doc.fill"
         case .diary:   return "pencil"
+        case .symptom: return "waveform.path.ecg"
         }
     }
     var accent: Color {
@@ -30,6 +33,7 @@ enum RecordKind: String, Identifiable, CaseIterable {
         case .quick:   return Tj.Palette.brick
         case .archive: return Tj.Palette.ink
         case .diary:   return Tj.Palette.leaf
+        case .symptom: return Tj.Palette.amber
         }
     }
 }
@@ -98,7 +102,7 @@ struct RecordSheet: View {
                 .clipShape(RoundedRectangle(cornerRadius: Tj.Radius.xl, style: .continuous))
                 .ignoresSafeArea(edges: .bottom)
         )
-        .presentationDetents([.fraction(0.55)])
+        .presentationDetents([.fraction(0.68)])
         .presentationDragIndicator(.hidden)
         .presentationBackground(Tj.Palette.sand)
         .presentationCornerRadius(Tj.Radius.xl)