Replace fragile index-based file selection with direct pointer binding
via g_object_set_data on listbox rows in both UnitsView and ShellsView.
Add Refresh buttons to all three tabs (Units, Shells, Plans). Add status
bar notifications for shell and plan file loads. Wrap control panels in
labeled GtkFrame containers across all tabs. Improve config tab layout
with better typography, spacing, width constraint, and resolved path
status indicators.
- Reorder tabs: Rex Config, Units, Plans, Shells
- Beautify Units, Plans, Shells, and Config tabs with framed lists,
linked button groups, consistent margins, and dim labels
- Grey out plan controls and task properties when no plan/task loaded
- Restructure shells from single-file to multi-file directory model,
paralleling the units architecture (create/delete/save files,
create/delete/edit/move shells within files)
- Fix shells loading to scan directories for .shells files
- Beautify unit properties dialog with GtkFrame sections, dim-label
field labels, internal padding, and linked file action buttons
- Add rectifier Select/Open/Create file buttons
- Fix GtkSwitch multi-click issue using state-set signal
- Move Save File button to unit files sidebar
- Sync unit editor state after name changes in properties dialog
