feat: add shell integration setup for fastfetch

[mateuszkozako]

Type of Change

• Refactoring

Description

Enhanced RC file detection in fastfetch-setup.sh by implementing a fallback mechanism to search for shell configuration files in the home directory. This improvement helps handle cases where RC files might be named differently or located in non-standard locations within $HOME.

Key changes:

• Added fallback search for .bashrc and .bash_profile in $HOME for bash
• Added fallback search for .zshrc in $HOME for zsh
• Improved error handling for cases when no RC file is found

Testing

• Tested with bash and zsh shells
• Verified fallback search works when default RC files are not present
• Confirmed proper error handling when no RC files are found
• Tested with different RC file configurations (.bashrc, .bash_profile)

Impact

• Improved reliability of shell configuration
• No new dependencies added
• Maintains backward compatibility
• Better user experience with more robust RC file detection

Issues / other PRs related

• Resolves #[Issue number for RC file detection enhancement]

Additional Information

The changes are focused on improving the robustness of RC file detection while maintaining the existing functionality and user experience.

Checklist

• My code adheres to the coding and style guidelines of the project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no errors/warnings/merge conflicts.