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>

FeelsWidget2/Assets.xcassets/WidgetBackground.colorset/Contents.json

@@ -0,0 +1,38 @@
+{
+  "colors" : [
+    {
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "1.000",
+          "green" : "1.000",
+          "red" : "1.000"
+        }
+      },
+      "idiom" : "universal"
+    },
+    {
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ],
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "0.000",
+          "green" : "0.000",
+          "red" : "0.000"
+        }
+      },
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}