[Jens-Olaf-Mueller]

This adds responsive progress feedback for loading and renaming large file lists.

Changes:

• add a progress bar next to the file toolbar
• process loading and renaming incrementally via GLib.idle_add()
• keep the GTK UI responsive during long operations
• show progress as current / total
• temporarily disable file controls while processing
• prevent parallel load/rename jobs from drag-and-drop, keyboard shortcuts or toolbar actions
• restore UI state correctly after completion or errors
• update bulky.pot with the new translatable progress strings

Tested successfully with:

• 2,033 files
• 4,307 files
• repeated loading
• repeated renaming
• toolbar locking during active operations

[clefebvre]

Hi @Jens-Olaf-Mueller,

I think tackling the UI freeze is needed but the progressbar isn't. Most operations are small, this adds visual complexity to something that should be simple. I'll close this but tackle the threading problem on master. I'll also tackle the fact that the loading of the app is single-threaded.