Improve subscription UI and fix trial date handling

Lock Screen:
- Add light/dark mode support with adaptive colors
- Make passcode text tappable to trigger authentication

Trial Date Fixes:
- Fix IAPManager to read firstLaunchDate directly from UserDefaults
- Add expiration date check (> Date()) before showing "expires in" text
- Show "Trial expired" when trial end date is in the past
- Disable subscription bypass in DEBUG mode for testing

Month/Year Subscribe Prompts:
- Redesign with gradient icons and compelling copy
- Add fade mask (100% at top to 0% at 50%) for content behind
- Position subscribe overlay on bottom half of screen
- Month: purple/pink theme with calendar icon
- Year: orange/pink theme with chart icon

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

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

Shared/Views/PurchaseButtonView.swift

@@ -180,8 +180,12 @@ struct PurchaseButtonView: View {
             Image(systemName: "clock")
                 .foregroundColor(.orange)
 
-            if let expirationDate = iapManager.trialExpirationDate {
+            if let expirationDate = iapManager.trialExpirationDate, expirationDate > Date() {
                 Text("\(Text(String(localized: "purchase_view_trial_expires_in")).foregroundColor(textColor)) \(Text(expirationDate, style: .relative).foregroundColor(.orange).bold())")
+            } else {
+                Text(String(localized: "purchase_view_trial_expired"))
+                    .foregroundColor(.orange)
+                    .bold()
             }
         }
         .font(.body)