PHASE6-008. (feat) Offline-First Reliability

Implemented:
3.1 Connectivity Indicator - Badge in app bar (Green/Gray/Orange)
3.2 Sync Queue UI - Pending count with dialog
3.3 Manual Sync Button - Loading state + success snackbar
3.4 Conflict Resolution UI - Dialog with local vs remote
3.5 Offline Tutorial - 4-page animated walkthrough

Files:
- connectivity_badge.dart: NEW
- sync_queue_status.dart: NEW
- conflict_resolution_dialog.dart: NEW
- offline_tutorial_dialog.dart: NEW
- app_shell.dart: Integrated badge
- parent_dashboard_screen.dart: Sync UI
- pubspec.yaml: Added connectivity_plus

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

Author: xronocode