Fix build errors, resolve all warnings, and improve code quality

Widget Extension Fixes:
- Create standalone WidgetDataProvider for widget data isolation
- Add WIDGET_EXTENSION compiler flag for conditional compilation
- Fix DataController references in widget-shared files
- Sync widget version numbers with main app (23, 1.0.2)
- Add WidgetBackground color to asset catalog

Warning Resolutions:
- Fix UIScreen.main deprecation in BGView and SharingListView
- Fix Text '+' concatenation deprecation in PurchaseButtonView and SettingsTabView
- Fix exhaustive switch in BiometricAuthManager (add .none case)
- Fix var to let in ExportService (3 instances)
- Fix unused result warning in NoteEditorView
- Fix ForEach duplicate ID warnings in MonthView and YearView

Code Quality Improvements:
- Wrap bypassSubscription in #if DEBUG for security
- Rename StupidAssCustomWidgetObservableObject to CustomWidgetStateViewModel
- Add @MainActor to IconViewModel
- Replace fatalError with graceful fallback in SharedModelContainer
- Add [weak self] to closures in DayViewViewModel
- Add OSLog-based AppLogger for production logging
- Add ImageCache with NSCache for memory efficiency
- Add AccessibilityHelpers with Reduce Motion support
- Create DataControllerProtocol for dependency injection
- Update .gitignore with secrets exclusions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -66,3 +66,11 @@ fastlane/report.xml
 fastlane/Preview.html
 fastlane/screenshots/**/*.png
 fastlane/test_output
+
+# Secrets and API Keys
+GoogleService-Info.plist
+**/GoogleService-Info.plist
+*.xcconfig
+!*.xcconfig.template
+Secrets.swift
+**/Secrets.swift