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/RootView.swift

@@ -1,19 +1,21 @@
 import SwiftUI
 
 enum TjTab: String, Hashable, CaseIterable {
-    case home, trend, me
+    case home, records, trend, me
     var label: String {
         switch self {
-        case .home:  return "首页"
-        case .trend: return "趋势"
-        case .me:    return "我的"
+        case .home:    return "主页"
+        case .records: return "记录"
+        case .trend:   return "趋势"
+        case .me:      return "我的"
         }
     }
     var icon: String {
         switch self {
-        case .home:  return "house"
-        case .trend: return "chart.line.uptrend.xyaxis"
-        case .me:    return "person.circle"
+        case .home:    return "house"
+        case .records: return "list.bullet.rectangle"
+        case .trend:   return "chart.line.uptrend.xyaxis"
+        case .me:      return "person.circle"
         }
     }
 }
@@ -27,14 +29,16 @@ struct RootView: View {
     @State private var tab: TjTab = .home
     @State private var showRecordSheet = false
     @State private var activeFlow: ActiveFlow?
+    @State private var showSymptomStart = false
 
     var body: some View {
         VStack(spacing: 0) {
             Group {
                 switch tab {
-                case .home:  HomeView(onTapArchive: {})
-                case .trend: TrendsView()
-                case .me:    MeView()
+                case .home:    HomeView(onTapArchive: { tab = .records })
+                case .records: ArchiveListView()
+                case .trend:   TrendsView()
+                case .me:      MeView()
                 }
             }
             .frame(maxWidth: .infinity, maxHeight: .infinity)
@@ -51,11 +55,15 @@ struct RootView: View {
                     switch kind {
                     case .quick:   activeFlow = .quick
                     case .archive: activeFlow = .archive
+                    case .symptom: showSymptomStart = true
                     case .diary:   break
                     }
                 }
             }
         }
+        .sheet(isPresented: $showSymptomStart) {
+            SymptomStartSheet()
+        }
 #if os(iOS)
         .fullScreenCover(item: $activeFlow) { flow in
             switch flow {
@@ -83,66 +91,101 @@ private struct TabBar: View {
     let onTap: (TjTab) -> Void
     let onTapRecord: () -> Void
 
+    private let cornerRadius: CGFloat = 22
+    private let slotHeight: CGFloat = 34
+
     var body: some View {
-        HStack(spacing: 0) {
+        HStack(alignment: .bottom, spacing: 0) {
             tabItem(.home)
-            Color.clear.frame(width: 60, height: 1)
+            tabItem(.records)
+            recordSlot
             tabItem(.trend)
             tabItem(.me)
         }
-        .padding(.horizontal, 12)
+        .padding(.horizontal, 4)
         .padding(.top, 10)
-        .padding(.bottom, 4)
-        .background(
-            Tj.Palette.paper
-                .overlay(alignment: .top) {
-                    Rectangle()
-                        .fill(Tj.Palette.lineSoft)
-                        .frame(height: 1)
-                }
+        .padding(.bottom, 6)
+        .background(barBackground)
+    }
+
+    private var barBackground: some View {
+        UnevenRoundedRectangle(
+            topLeadingRadius: cornerRadius,
+            bottomLeadingRadius: 0,
+            bottomTrailingRadius: 0,
+            topTrailingRadius: cornerRadius,
+            style: .continuous
         )
+        .fill(Tj.Palette.paper)
         .overlay(alignment: .top) {
-            recordButton.offset(y: -22)
+            Rectangle()
+                .fill(Tj.Palette.lineSoft)
+                .frame(height: 1)
         }
+        .shadow(color: Tj.Palette.ink.opacity(0.05), radius: 10, x: 0, y: -2)
     }
 
     private func tabItem(_ t: TjTab) -> some View {
-        Button { onTap(t) } label: {
+        let isActive = active == t
+        return Button { onTap(t) } label: {
             VStack(spacing: 4) {
-                Image(systemName: t.icon)
-                    .font(.system(size: 20, weight: .regular))
-                    .frame(width: 26, height: 26)
+                ZStack {
+                    if isActive {
+                        Capsule()
+                            .fill(Tj.Palette.sand2)
+                            .frame(width: 44, height: slotHeight - 6)
+                    }
+                    Image(systemName: t.icon)
+                        .font(.system(size: 18, weight: isActive ? .semibold : .regular))
+                }
+                .frame(width: 50, height: slotHeight)
+
                 Text(t.label)
-                    .font(.system(size: 11))
+                    .font(.system(size: 11, weight: isActive ? .semibold : .regular))
             }
-            .foregroundStyle(active == t ? Tj.Palette.ink : Tj.Palette.text3)
+            .foregroundStyle(isActive ? Tj.Palette.ink : Tj.Palette.text3)
             .frame(maxWidth: .infinity)
-            .padding(.vertical, 4)
             .contentShape(Rectangle())
         }
-        .buttonStyle(.plain)
+        .buttonStyle(TabPressStyle())
     }
 
-    private var recordButton: some View {
+    private var recordSlot: some View {
         Button(action: onTapRecord) {
             VStack(spacing: 4) {
                 ZStack {
                     Circle()
                         .fill(Tj.Palette.ink)
-                        .shadow(color: Color(red: 0.157, green: 0.216, blue: 0.176).opacity(0.25),
-                                radius: 12, x: 0, y: 4)
+                        .overlay(
+                            Circle()
+                                .strokeBorder(Tj.Palette.paper, lineWidth: 2)
+                        )
+                        .shadow(color: Tj.Palette.ink.opacity(0.18),
+                                radius: 4, x: 0, y: 2)
+
                     Image(systemName: "plus")
-                        .font(.system(size: 20, weight: .semibold))
+                        .font(.system(size: 16, weight: .semibold))
                         .foregroundStyle(Tj.Palette.paper)
                 }
-                .frame(width: 52, height: 52)
+                .frame(width: slotHeight, height: slotHeight)
 
-                Text("记录")
-                    .font(.system(size: 11))
+                Text("新建")
+                    .font(.system(size: 11, weight: .semibold))
                     .foregroundStyle(Tj.Palette.ink)
             }
+            .frame(maxWidth: .infinity)
+            .contentShape(Rectangle())
         }
-        .buttonStyle(.plain)
+        .buttonStyle(TabPressStyle())
+    }
+}
+
+private struct TabPressStyle: ButtonStyle {
+    func makeBody(configuration: Configuration) -> some View {
+        configuration.label
+            .scaleEffect(configuration.isPressed ? 0.92 : 1.0)
+            .animation(.spring(response: 0.25, dampingFraction: 0.7),
+                       value: configuration.isPressed)
     }
 }