Multiple keyboard shortcuts (Remove item, Move Up/Down, etc) missing with AppImage

**Describe the bug**
Several application keyboard shortcuts do not work when using the AppImage package. In fact, preferences show these shortcuts are simply not defined, although they are with other formats like Flatpak and .deb.

The screenshots below show 16 missing shortcuts, including _Sort Selected Items_ and _Cancel Editing_. It is unclear what these would have in common.

**To Reproduce**
1. Launch CopyQ ($ ./CopyQ-*.AppImage;) with default configuration
2. Open the main window
3. Select an item to delete
4. Press Del

**Expected behavior**
The item is deleted.

**Actual behavior**
Nothing happens.

**Screenshots**
Flatpak left, AppImage right, both at 16.0:

**Version, OS and Environment**
CopyQ 16.0.0
Arch: x86_64-little_endian-lp64
Audio: miniaudio 0.11.25
Compiler: GCC
DISPLAY: :0
KGuiAddons: 6.27.0
KNotifications: 6.27.0
KStatusNotifierItem: 6.27.0
OS: Debian GNU/Linux 13 (trixie)
QCA: 2.3.10
Qt: 6.11.1
QtKeychain: 0.15.0
XDG_CURRENT_DESKTOP: KDE
XDG_SESSION_DESKTOP: KDE
XDG_SESSION_TYPE: x11
has-audio: 1
has-encryption: 1
has-global-shortcuts: 1
has-keychain: 1
has-mouse-selection: 1

**Additional context**
The only thing logs show is the warning reported in #3631.

This can be seen with both installs running simultaneously, as the _Screenshots_ section shows. This happens whether or not another CopyQ instance is running when CopyQ is started or when shortcuts are attempted.

[🅭🄍](https://www.philippecloutier.com/Common+infrastructure+licensing#its)

Reproduce the missing shortcuts with the CopyQ 16.0 AppImage, then compare the shortcut definitions with the Flatpak and .deb installs. Start by tracing where application shortcuts are defined or loaded and review the warning referenced in #3631. Done means the affected shortcuts, including Del for removing an item, are defined and work in the AppImage.

Written by the indexing model from the issue text.