[WIP] Ads Integration for Free Tier and Pro Entitlement Removal

[Copilot]

• Analyze repository structure and understand existing premium system
• Review current subscription/payment infrastructure (product IDs, premium upgrade screen)
• Identify existing local storage patterns (SharedPreferences via ThemeService)
• Add AdMob dependencies to pubspec.yaml (google_mobile_ads, app_tracking_transparency, in_app_purchase)
• Create subscription service to track Pro entitlements with purchase verification
• Create ads service for banner/interstitial ad management with rate limiting
• Create consent service for ATT (iOS) and GDPR/UMP (Android) compliance
• Add ad unit ID configuration with secure rotation (AdConfig model)
• Create ads analytics service for tracking metrics (impressions, CTR, ARPDAU)
• Update Android manifest and iOS plist for ad permissions and AdMob app ID
• Create ad banner widgets with premium user checking
• Initialize all services in main.dart with proper dependency injection
• Integrate ads display logic in main screens (dashboard, editor)
• Update premium upgrade screen to handle ad removal
• Test consent flows and ad compliance across regions

Added comprehensive ads infrastructure including:

• SubscriptionService: Tracks Pro status with 24h verification cycle and debug toggles
• ConsentService: Handles ATT/GDPR consent with proper platform detection
• AdsService: Manages banner/interstitial ads with subscription checking and rate limiting
• AdConfig: Secure ad unit ID rotation with regional restrictions
• AdsAnalyticsService: Comprehensive tracking (CTR, ARPDAU, user segmentation)
• AdBannerWidget: Smart banner display with premium upgrade prompts
• Platform permissions and AdMob app ID configuration

Next: Integrate into UI screens and test functionality.

Fixes #31.

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