Add HealthBridge iOS app for intelligent health data synchronization

Complete implementation of a SwiftUI iOS app that serves as a "Single Source
of Truth" for health data. The app reads from all Apple Health sources,
detects conflicts between devices, merges data using configurable strategies,
and writes cleaned data back.

Features:
- Phase 1: HealthKit integration with automatic source discovery
- Phase 2: DataReader with conflict detection (time-window based)
- Phase 3: RuleEngine with 8 merge strategies (exclusive, priority, higher wins, etc.)
- Phase 4: MergeEngine for conflict resolution + DataWriter for HealthKit writes
- Phase 5: SwiftUI UI for dashboard, conflicts, rules, and sources management
- Phase 6: Background sync with configurable intervals and push notifications
- Phase 7: Complete rule editor and polished UI components

Supported data types:
- Steps, Heart Rate, Blood Pressure, SpO2, Sleep
- Distance, Floors Climbed, Active Energy, HRV, Respiratory Rate

Architecture: SourceManager -> DataReader -> RuleEngine -> MergeEngine -> DataWriter

HealthBridge/Utils/Extensions.swift

@@ -0,0 +1,153 @@
+import Foundation
+import SwiftUI
+
+// MARK: - Date Extensions
+extension Date {
+    var startOfDay: Date {
+        Calendar.current.startOfDay(for: self)
+    }
+
+    var endOfDay: Date {
+        Calendar.current.date(byAdding: .day, value: 1, to: startOfDay)!.addingTimeInterval(-1)
+    }
+
+    var isToday: Bool {
+        Calendar.current.isDateInToday(self)
+    }
+
+    var isYesterday: Bool {
+        Calendar.current.isDateInYesterday(self)
+    }
+
+    func formatted(style: DateFormatter.Style) -> String {
+        let formatter = DateFormatter()
+        formatter.dateStyle = style
+        formatter.timeStyle = .none
+        return formatter.string(from: self)
+    }
+
+    func formattedTime() -> String {
+        let formatter = DateFormatter()
+        formatter.dateStyle = .none
+        formatter.timeStyle = .short
+        return formatter.string(from: self)
+    }
+
+    func formattedRelative() -> String {
+        let formatter = RelativeDateTimeFormatter()
+        formatter.unitsStyle = .abbreviated
+        return formatter.localizedString(for: self, relativeTo: Date())
+    }
+
+    func adding(days: Int) -> Date {
+        Calendar.current.date(byAdding: .day, value: days, to: self)!
+    }
+
+    func adding(hours: Int) -> Date {
+        Calendar.current.date(byAdding: .hour, value: hours, to: self)!
+    }
+
+    func adding(minutes: Int) -> Date {
+        Calendar.current.date(byAdding: .minute, value: minutes, to: self)!
+    }
+}
+
+// MARK: - Double Extensions
+extension Double {
+    func formatted(decimals: Int = 1) -> String {
+        String(format: "%.\(decimals)f", self)
+    }
+
+    var formattedAsInteger: String {
+        String(format: "%.0f", self)
+    }
+
+    var formattedAsPercentage: String {
+        String(format: "%.1f%%", self * 100)
+    }
+}
+
+// MARK: - Array Extensions
+extension Array {
+    func chunked(into size: Int) -> [[Element]] {
+        stride(from: 0, to: count, by: size).map {
+            Array(self[$0..<Swift.min($0 + size, count)])
+        }
+    }
+}
+
+// MARK: - Color Extensions
+extension Color {
+    static let healthBridgePrimary = Color.blue
+    static let healthBridgeSecondary = Color.cyan
+    static let healthBridgeAccent = Color.orange
+
+    static func forSeverity(_ severity: ConflictSeverity) -> Color {
+        switch severity {
+        case .minor: return .green
+        case .moderate: return .yellow
+        case .significant: return .orange
+        case .major: return .red
+        }
+    }
+
+    static func forQuality(_ quality: DataQuality) -> Color {
+        switch quality {
+        case .complete: return .green
+        case .partial: return .yellow
+        case .missing: return .gray
+        case .invalid: return .red
+        }
+    }
+}
+
+// MARK: - View Extensions
+extension View {
+    func cardStyle() -> some View {
+        self
+            .padding()
+            .background(Color(.systemBackground))
+            .clipShape(RoundedRectangle(cornerRadius: 12))
+            .shadow(color: .black.opacity(0.05), radius: 4, y: 2)
+    }
+
+    func sectionHeader(_ title: String) -> some View {
+        VStack(alignment: .leading, spacing: 8) {
+            Text(title)
+                .font(.headline)
+                .foregroundStyle(.primary)
+            self
+        }
+    }
+}
+
+// MARK: - Binding Extensions
+extension Binding {
+    func onChange(_ handler: @escaping (Value) -> Void) -> Binding<Value> {
+        Binding(
+            get: { self.wrappedValue },
+            set: { newValue in
+                self.wrappedValue = newValue
+                handler(newValue)
+            }
+        )
+    }
+}
+
+// MARK: - Optional Extensions
+extension Optional where Wrapped == String {
+    var orEmpty: String {
+        self ?? ""
+    }
+
+    var isNilOrEmpty: Bool {
+        self?.isEmpty ?? true
+    }
+}
+
+// MARK: - Collection Extensions
+extension Collection {
+    var isNotEmpty: Bool {
+        !isEmpty
+    }
+}