Demo 02: Build Shell

Prompt file imported from AkashAi7/github-copilot-flutter-demo-kit (.github/prompts/demo-02-shell.prompt.md). Copyright stays with the author.

Implement the responsive application shell from the approved plan and business requirements.

Requirements:

• Keep main.dart as a small composition root.
• Add a purposeful Material 3 campus theme.
• Model student, department staff, and administrator roles.
• Use Riverpod to provide the current role.
• Use bottom navigation below 760 px and a navigation rail at wider sizes.
• Give each role suitable destinations and an overview with role-specific metrics.
• Add widget tests proving student navigation and administrator destinations.

Work autonomously, format changed Dart files, run flutter analyze and flutter test, and fix failures before summarizing the result.