Add full light and dark mode support for iOS and Android

This commit ensures both platforms properly support light and dark mode with automatic switching based on system settings.

## iOS Changes
- Updated DesignSystem.swift to use adaptive system colors
- Changed neutral colors to use UIKit system colors:
  - background: systemGroupedBackground
  - surface: secondarySystemGroupedBackground
  - text colors: label, secondaryLabel, tertiaryLabel
  - borders: separator, opaqueSeparator
- Colors now automatically adapt to light/dark mode
- Info.plist already configured to support both modes

## Android Changes
- Updated AndroidManifest.xml app theme
- Changed from Theme.Material.Light.NoActionBar to Theme.Material.NoActionBar
- Allows app to respect system dark mode settings
- Theme.kt already has complete light/dark color schemes
- MyCribTheme automatically switches based on system settings

## Testing
- iOS: Toggle Settings → Display & Brightness → Appearance
- Android: Toggle Settings → Display → Dark theme
- Both platforms automatically update colors

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

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

composeApp/src/androidMain/AndroidManifest.xml

@@ -17,7 +17,7 @@
         android:label="@string/app_name"
         android:roundIcon="@mipmap/ic_launcher_round"
         android:supportsRtl="true"
-        android:theme="@android:style/Theme.Material.Light.NoActionBar"
+        android:theme="@android:style/Theme.Material.NoActionBar"
         android:networkSecurityConfig="@xml/network_security_config">
         <activity
             android:exported="true"

iosApp/iosApp/Design/DesignSystem.swift

@@ -1,7 +1,7 @@
 import SwiftUI
 
 // MARK: - Design System
-// Modern, sleek design system for MyCrib
+// Modern, sleek design system for MyCrib with Light and Dark mode support
 
 struct AppColors {
     // Primary Colors - Modern blue gradient
@@ -19,17 +19,17 @@ struct AppColors {
     static let error = Color(hex: "EF4444") ?? .red
     static let info = Color(hex: "3B82F6") ?? .blue
 
-    // Neutral Colors - Modern grays
-    static let background = Color(hex: "F9FAFB") ?? Color(.systemGroupedBackground)
-    static let surface = Color.white
-    static let surfaceSecondary = Color(hex: "F3F4F6") ?? Color(.secondarySystemGroupedBackground)
+    // Adaptive Neutral Colors - Automatically adapt to light/dark mode
+    static let background = Color(uiColor: .systemGroupedBackground)
+    static let surface = Color(uiColor: .secondarySystemGroupedBackground)
+    static let surfaceSecondary = Color(uiColor: .tertiarySystemGroupedBackground)
 
-    static let textPrimary = Color(hex: "111827") ?? Color(.label)
-    static let textSecondary = Color(hex: "6B7280") ?? Color(.secondaryLabel)
-    static let textTertiary = Color(hex: "9CA3AF") ?? Color(.tertiaryLabel)
+    static let textPrimary = Color(uiColor: .label)
+    static let textSecondary = Color(uiColor: .secondaryLabel)
+    static let textTertiary = Color(uiColor: .tertiaryLabel)
 
-    static let border = Color(hex: "E5E7EB") ?? Color(.separator)
-    static let borderLight = Color(hex: "F3F4F6") ?? Color(.separator)
+    static let border = Color(uiColor: .separator)
+    static let borderLight = Color(uiColor: .opaqueSeparator)
 
     // Task Status Colors
     static let taskUpcoming = Color(hex: "3B82F6") ?? .blue