feat: iOS widgets + fix sleep showing yesterday's data

Widgets:
- HabitsProgressWidget (small/medium): progress ring, completed/total habits, tasks count
- HealthSummaryWidget (small/medium): readiness score, steps, sleep, heart rate
- Shared Keychain access group for app ↔ widget token sharing
- Widget data refreshes every 30 minutes

Sleep fix:
- Changed sleep window from "24 hours back" to "6 PM yesterday → now"
- Captures overnight sleep correctly without showing previous day's data
- Applied to both fetchSleepData (sync) and fetchSleepSegments (detail view)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

PulseWidget/PulseWidgetBundle.swift

@@ -0,0 +1,10 @@
+import WidgetKit
+import SwiftUI
+
+@main
+struct PulseWidgetBundle: WidgetBundle {
+    var body: some Widget {
+        HabitsProgressWidget()
+        HealthSummaryWidget()
+    }
+}