feat: add Clear Skies sample app for Shorebird FlutterCon live demo

[AbhishekDoshi26]

Description

This PR introduces Clear Skies, a beautifully designed, premium weather application built entirely from scratch to serve as a high-impact live demo for Shorebird at FlutterCon USA.

The app features an immersive glassmorphic UI, dynamic time-of-day background gradients, and zero-click onboarding utilizing native reverse-geocoding. Most importantly, this baseline release contains intentional, highly-visual bugs tagged with TODO(Demo) specifically meant to be patched live over the air during the Shorebird stage presentation.

✨ Key Features

• Premium Glassmorphic UI: Built with heavy use of BackdropFilter and refined typography (google_fonts Outfit and Inter).
• Dynamic Backgrounds: The UI automatically shifts between a vibrant daylight gradient and a deep midnight blue based on local weather time.
• Zero-Click Onboarding: Integrates geolocator and geocoding for native GPS coordinate retrieval and reverse-geocoding to display actual city names automatically.
• Popular Destinations Fallback: Elegant chips for instant 1-tap weather forecasts if location is disabled.
• Persistent Favorites: Save most-visited cities to a horizontal scrollable list, persisted locally via shared_preferences.
• Robust Architecture: Highly optimized, 60 FPS widget tree utilizing flutter_bloc for scalable state management.

🐛 The "FlutterCon" Bugs

Note: These bugs are intentional and meant to be shipped in the baseline APK.

• The Toxic Gradient: The daytime background gradient is currently a jarring, horrible mixture of Neon Green, Toxic Yellow, and Bright Red (app_colors.dart).
• The Typos: The app name and welcome strings say "Unclear Skies - Discover the world's worst weather" (app_strings.dart).
• The Antarctica Bug: Tapping the "Tokyo" popular destination chip actually requests the weather for Antarctica (welcome_hero_widget.dart).

During the demo, the presenter will simply search for TODO(Demo), revert these 3 files, and run shorebird patch android to fix the production app live in front of the audience.

🛠 Tech Stack

• flutter_bloc & bloc
• geolocator & geocoding
• shared_preferences
• http (fetching from Open-Meteo API)
• google_fonts

🧪 Testing

• The app includes a robust suite of over 70+ automated widget and unit tests ensuring stability across the bloc layer and the UI.
• All tests currently pass, mimicking a scenario where visual/logical bugs slip past CI/CD undetected.