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Tests/ModelsSchemaTests.swift

@@ -12,6 +12,7 @@ struct ModelsSchemaTests {
             DiaryEntry.self,
             Asset.self,
             ChatTurn.self,
+            Symptom.self,
         ])
         let config = ModelConfiguration(schema: schema, isStoredInMemoryOnly: true)
         return try ModelContainer(for: schema, configurations: [config])
@@ -58,6 +59,37 @@ struct ModelsSchemaTests {
         #expect(remaining.isEmpty)
     }
 
+    @Test func ongoingSymptomQueryFiltersByEndedAt() throws {
+        let container = try makeContainer()
+        let ctx = ModelContext(container)
+
+        let active = Symptom(name: "头痛", startedAt: .now.addingTimeInterval(-3600))
+        let ended = Symptom(
+            name: "咳嗽",
+            startedAt: .now.addingTimeInterval(-7200),
+            endedAt: .now.addingTimeInterval(-1800)
+        )
+        ctx.insert(active)
+        ctx.insert(ended)
+        try ctx.save()
+
+        let predicate = #Predicate<Symptom> { $0.endedAt == nil }
+        let ongoing = try ctx.fetch(FetchDescriptor<Symptom>(predicate: predicate))
+
+        #expect(ongoing.count == 1)
+        #expect(ongoing.first?.name == "头痛")
+        #expect(active.isOngoing)
+        #expect(!ended.isOngoing)
+        #expect(active.duration >= 3600)
+    }
+
+    @Test func symptomSeverityClampedToRange() throws {
+        let high = Symptom(name: "腹痛", severity: 99)
+        let low = Symptom(name: "失眠", severity: -3)
+        #expect(high.severity == 5)
+        #expect(low.severity == 1)
+    }
+
     @Test func chatTurnPersistsReferencedIDs() throws {
         let container = try makeContainer()
         let ctx = ModelContext(container)