rewrite: app.py Phase 3-C — action definitions (menu items)

[wkentaro]

Summary

Rewrites the action definitions section of labelme/app.py (lines ~248–412) to use consistent explicit keyword arguments throughout.

What changed

All action() calls in the menu-action setup block now use explicit keyword parameters (text=, slot=, shortcut=, icon=, tip=, etc.) instead of a mix of positional and keyword arguments.

Affected actions:

• quit, open_, opendir, openNextImg, openPrevImg
• save, saveAs, deleteFile, changeOutputDir
• saveAuto, saveWithImageData, close
• toggle_keep_prev_mode
• createMode, createRectangleMode, createCircleMode, createLineMode, createPointMode, createLineStripMode

Behavior

No functional change. All tr() strings, shortcuts, icons, and callbacks are identical to before. The saveAuto lambda parameter was renamed from x to checked for clarity.

Tests

36 unit tests pass (python3 -m pytest tests/unit/ -k "not qapp").

[wkentaro]

Closing in favor of a more meaningful refactor. Rather than just rewriting variable assignments in place, we're restructuring __init__ (~850 lines) into focused private setup methods (_setup_widgets, _setup_actions, _setup_menus, etc.), which serves the dual-license goal while producing genuinely cleaner code. Will open a new PR.