Port GooCanvas to native GTK3/Cairo drawing

[bgermann]

Replace all GooCanvas-based canvas widgets with GtkDrawingArea and Cairo for rendering satellite tracking visualizations:

• gtk-polar-view: Polar plot for real-time satellite tracking
• gtk-polar-plot: Polar plot for pass visualization
• gtk-azel-plot: Azimuth/Elevation time plot
• gtk-sat-map: World map with satellite positions and ground tracks
• gtk-sky-glance: Timeline view of upcoming passes

Key changes:

• Replace GooCanvasItemModel objects with coordinate fields in structs
• Implement on_draw() callbacks using Cairo API for all rendering
• Add manual hit testing for mouse interactions
• Store render state (points, colors, positions) in widget structures
• Use gtk_widget_queue_draw() to trigger redraws

Build system updates:

• Remove goocanvas-2.0/3.0 pkg-config checks from configure.ac
• Add explicit gtk+-3.0 dependency check
• Update CI workflows and snap

This eliminates the external GooCanvas library dependency, reducing build complexity and improving portability. The application now only requires GTK+ 3.0 and standard system libraries.

Fixes: #369

[csete]

Thank you much @bgermann - this is a huge help :)

I am going to merge it into the master branch. Although I noticed a few things that will have to be fixed, I think it is best to move ahead based on this work.

Thanks again!