analytics(healthkit): wire historical HealthKit reference into reports (KC-51 ph4e)

Completes 'available HealthKit trends' for weekly/monthly reports. Adds
HealthKitManager.dailyReference (3 parallel bucketed HKStatisticsCollectionQuery
for steps/active-calories/resting-HR over ~13 months), AnalyticsService.
refreshHealthReference to cache and merge it into DaySamples, and avgSteps/
avgActiveCalories/avgRestingHR on PeriodSummary (nil when absent — honest).
Surfaced in AnalyticsView's weekly/monthly cards.

Verified standalone (swiftc, 8/8): aggregation correct when present, nil when
absent, workout metrics unaffected, reports stay deterministic. Tests added to
AnalyticsEngineTests. This completes all analytics logic — remaining work is the
first Xcode build (device, user-run) to catch any SwiftUI compile issues.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

KisaniCalTests/AnalyticsEngineTests.swift

@@ -170,6 +170,30 @@ final class AnalyticsEngineTests: XCTestCase {
         XCTAssertEqual(s.consistency, 2.0/3.0, accuracy: 0.0001)
     }
 
+    // MARK: - HealthKit reference aggregation (partial/missing data honest)
+
+    func testSummarizeAggregatesHealthKitAveragesWhenPresent() {
+        let days = [
+            DaySample(dateKey: "2026-07-06", didWorkout: true, scheduled: true, sessions: 1, sets: 20, volume: 1000,
+                      steps: 8000, activeCalories: 500, restingHeartRate: 55),
+            DaySample(dateKey: "2026-07-07", didWorkout: true, scheduled: true, sessions: 1, sets: 18, volume: 900,
+                      steps: 10000, activeCalories: 600, restingHeartRate: 57),
+            DaySample(dateKey: "2026-07-08", didWorkout: false, scheduled: false) // no HK reference
+        ]
+        let s = AnalyticsEngine.summarize(days)
+        XCTAssertEqual(s.avgSteps, 9000)
+        XCTAssertEqual(s.avgActiveCalories, 550)
+        XCTAssertEqual(s.avgRestingHR, 56)
+    }
+
+    func testSummarizeHealthKitNilWhenAbsent() {
+        let s = AnalyticsEngine.summarize([DaySample(dateKey: "2026-07-06", didWorkout: true, scheduled: true, sets: 20, volume: 1000)])
+        XCTAssertNil(s.avgSteps)
+        XCTAssertNil(s.avgActiveCalories)
+        XCTAssertNil(s.avgRestingHR)
+        XCTAssertEqual(s.volume, 1000)   // workout metrics unaffected
+    }
+
     // MARK: - Reports (idempotency / determinism)
 
     func testWeeklyReportDeterministic() {