Migrate iOS app to system colors and improve UI/UX

- Remove AppColors struct, migrate to iOS system colors throughout
- Redesign ContractorFormSheet to use native SwiftUI Form components
- Add color-coded icons to contractor form sections
- Improve dark mode contrast for task cards
- Add background colors to document detail fields
- Fix text alignment issues in ContractorDetailView
- Make task completion lists expandable/collapsible by default
- Clear app badge on launch and when app becomes active
- Update button styling with proper gradients and shadows
- Improve form field focus states and accessibility

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

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

iosApp/iosApp/Subviews/Task/CompletionCardView.swift

@@ -36,7 +36,7 @@ struct CompletionCardView: View {
                 HStack(alignment: .top, spacing: 6) {
                     Image(systemName: "wrench.and.screwdriver")
                         .font(.caption2)
-                        .foregroundColor(AppColors.primary)
+                        .foregroundColor(.blue)
 
                     VStack(alignment: .leading, spacing: 2) {
                         Text("By: \(contractorDetails.name)")