[FEATURE] Let users pick the text-injection backend (e.g. force wtype instead of IBus) #476

🚀 Feature Description

Let users pick the text-injection backend — e.g. force wtype instead of IBus on Wayland. Right now there's no way to tell vocalinux which one to use.

💡 Problem Statement

On Wayland, vocalinux always goes for IBus when it's available, and there's no way to tell it not to. That's a problem on compositors where IBus doesn't actually deliver text to native apps.

My case: Pop!_OS with COSMIC. IBus injection works in XWayland stuff (browser, vocalinux's own field) but nothing shows up in native Wayland apps like the COSMIC editor or Zed. wtype works perfectly on the same machine, German umlauts and all. But I can't get vocalinux onto wtype, and there's no override to make it happen.

📋 Proposed Solution

An explicit backend override like an injection_backend key in the existing config.json. When set to a non-IBus backend, vocalinux would skip the IBus path entirely and not start ibus-daemon. Left unset, everything stays exactly as it is now.

🔄 Alternatives Considered

• Removing IBus — not an option, there are other dependencies.
• Killing ibus-daemon first — doesn't help, vocalinux just restarts it once it picks the IBus path.

✅ Acceptance Criteria

• A config to select injection backend.
• When set to a non-IBus backend, vocalinux doesn't enter the IBus path or start ibus-daemon.
• When unset, current auto-detection behavior is unchanged.