* fix: improve Debian/pipx installation experience
- Enhanced error messages in check_dependencies() to provide distro-specific
installation commands (Ubuntu/Debian, Fedora, Arch Linux)
- Added explicit pipx guidance: install system packages BEFORE pipx install
- Updated error message to use gir1.2-ayatanaappindicator3-0.1 for Debian
- Added comprehensive pipx installation section to DISTRO_COMPATIBILITY.md
with step-by-step instructions for all major distributions
* fix: add display availability check to prevent GTK crash on Debian
The original PR only added documentation and improved error messages.
This commit adds the actual fix for issue #288.
Root cause: On some systems (especially Debian), GTK widgets can be
created before the display connection is properly established, causing
the crash: gtk_widget_get_scale_factor: assertion 'GTK_IS_WIDGET (widget)' failed
Fix: Add check_display_available() function that verifies Gdk.Display
is available before any GTK widgets are created. This provides a clear
error message instead of a cryptic GTK crash.
Fixes#288