Enhance markdown link support in tips and improve styling for better visibility

[rajbos]

This pull request updates the Copilot user tips and fluency guidance in src/extension.ts to include direct links to relevant VS Code Copilot documentation. This improves the user experience by making it easier for users to access help and learn about advanced features directly from the tips shown in the extension.

Most important changes:

Enhanced Tips and Guidance with Documentation Links

• Updated all Copilot usage tips (e.g., for agent mode, slash commands, model switching, context references, MCP servers, and customization) to include direct hyperlinks to the official VS Code Copilot documentation, making it easier for users to learn more about each feature. [1] [2] [3] [4] [5] [6] [7] [8]

Fluency Level Data Improvements

• Updated the getFluencyLevelData method to ensure all user guidance tips for each fluency level also include relevant documentation links for deeper learning and onboarding. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

These changes make the extension's tips more actionable and help users discover advanced Copilot features more efficiently.