Add kwin-libei backend

[jinliu]

KWin provides a libEI dbus interface, which requires no setup. Using it as the default input backend on KDE Plasma.

libEI wrapper code is from https://github.com/isac322/kwin-mcp

[Copilot]

Pull request overview

Adds a new KDE Plasma default input backend that injects input via KWin’s EIS D-Bus interface using libei, with fallback to the existing uinput backend elsewhere.

Changes:

• Introduces a new KWinLibeiBackend and low-level EISClient (libei + KWin EIS D-Bus).
• Updates backend selection to prefer KWin/libei on KDE Plasma and adds backend shutdown on quit.
• Updates build/install and README dependency documentation to include the new module and D-Bus Python bindings.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
vboard/window.py	Selects KWin/libei backend on KDE; calls backend.close() on quit.
vboard/libei.py	New libei + KWin EIS D-Bus client implementation.
vboard/input_backends.py	Adds KWinLibeiBackend; refactors key map to a module constant; adds close() hook.
meson.build	Installs the new vboard/libei.py module.
README.md	Documents extra dependency (python3-dbus) and notes uinput requirements by desktop.

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[archisman-panigrahi]

Thanks for the PR. How do I test this? What is the use case?

[jinliu]

It should work in KDE without needing to set up uinput. It talks to kwin via a private dbus interface.
No difference in other desktops.

[archisman-panigrahi]

Sorry, again, about the delay. Does this give any additional improvement over the uinput backend? I don't want to make the app overcomplicated unless it really helps a lot.

[jinliu]

No. The only advantage is not having to setup uinput access.

And it's totally fine if you don't want this. Most work is done by the kwin-mcp project. I just did a little bridging work.