chore: finalize Clear Skies demo prep, fix CI, and establish CODEOWNERS

[AbhishekDoshi26]

Description

This PR finalizes the preparation for the Clear Skies Shorebird FlutterCon live demo. It introduces a streamlined presenter workflow, integrates the sample into our CI pipeline, and sets up repository-wide PR reviewer defaults.

✨ Key Changes

• Streamlined Live Demo Workflow:
  • Refactored the intentional bugs in app_colors.dart, app_strings.dart, and welcome_hero_widget.dart. Instead of forcing the presenter to manually rewrite code on stage, the files now contain clearly marked // -- BUG VERSION -- and // -- CORRECT VERSION -- blocks. The presenter simply comments/uncomments the blocks.
• FlutterCon Demo Guide:
  • Added clear_skies/FLUTTERCON_DEMO.md to serve as the definitive playbook for anyone presenting the demo. It includes setup instructions, the presentation script, and a specific guide for resetting the app for continuous booth demo loops.
• CI Integration:
  • Registered the clear_skies project in .github/workflows/shorebird_ci.yaml. shorebird_ci verify now correctly identifies and builds the project on every PR.
• Test Suite Fixes:
  • Fixed a failing unit test in weather_helper_test.dart that was asserting an outdated fog emoji. (All 70 tests are now passing).
• CODEOWNERS Setup:
  • Added a .github/CODEOWNERS file at the root level to designate @AbhishekDoshi26 as the default reviewer, ensuring all future PRs across the repository are automatically assigned to the maintainer.

🧪 Verification

• shorebird_ci verify runs successfully and no longer reports clear_skies as MISSING.
• flutter test executes with 100% pass rate locally.