Improve clarity of output messages for link and unlink commands

[anitoanto]

This pull request updates GitDirector's messaging, documentation, and user interface to improve clarity and consistency, especially around the concept of "linking" repositories. It also enhances the TUI dashboard's handling of empty states and refines test cases to match the new terminology. Additionally, the project description and metadata have been updated for greater accuracy.

User experience and messaging improvements:

• Standardized terminology from "tracked" to "linked" across CLI commands, TUI dashboard, and test outputs for clarity [1] [2] [3] [4] [5] [6] [7] [8] [9].
• Improved TUI dashboard to show a clear "No repositories linked" message and instructions when no repos are present [1] [2] [3].

Documentation and metadata updates:

• Revised project descriptions in README.md, pyproject.toml, and gitdirector.rb to better reflect the tool's features and focus on multi-repo developer workflows [1] [2] [3].
• Added more detailed usage instructions and feature list for the TUI console in the documentation.

Code and test refinements:

• Improved feedback in CLI commands: now lists all newly linked repositories and only displays removed repos during unlink operations [1] [2].
• Updated and refined test cases to match new output messages and terminology [1] [2] [3].

Project metadata:

• Added new PyPI classifiers to better categorize the project.

These changes collectively improve user clarity, onboarding, and the overall developer experience with GitDirector.