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/SettingsView/SettingsTabView.swift

@@ -95,7 +95,7 @@ struct UpgradeBannerView: View {
                     .font(.subheadline.weight(.medium))
                     .foregroundColor(.orange)
 
-                if let expirationDate = trialExpirationDate {
+                if let expirationDate = trialExpirationDate, expirationDate > Date() {
                     Text("\(Text("Trial expires in ").font(.subheadline.weight(.medium)).foregroundColor(textColor.opacity(0.8)))\(Text(expirationDate, style: .relative).font(.subheadline.weight(.bold)).foregroundColor(.orange))")
                 } else {
                     Text("Trial expired")