feat: opt-in keyboard hotplug via keyboard_device_names allowlist

[mmacpherson]

adds pyudev-based keyboard hotplug detection. mirrors the existing device_monitor.py pattern (which already watches subsystem='sound' for microphone hotplug) with a new keyboard_monitor.py that watches subsystem='input'.

the problem: _discover_keyboards() runs once at startup, so a keyboard plugged in later (docking a laptop, bluetooth reconnecting) is invisible until the service restarts. surfaced for me on a usb-c dock with an external keyboard.

opt-in design: a non-nil keyboard_device_names allowlist is the single switch.

• null (default) = legacy behavior, byte-identical to current upstream.
• set it, and two things happen: (1) startup discovery is filtered to listed devices only, (2) the pyudev observer starts, attaching listed devices plugged in later.

why gate on the allowlist: some input devices pass the target_keys.issubset(available_keys) capability filter without being keyboards. E.g. the logitech m720 triathlon mouse advertises 162 EV_KEY codes including super, alt, and common letters. without the allowlist, aggressive hotplug grabs these and breaks mouse operation after a dock cycle. making the allowlist the opt-in switch couples the two correctly: by listing real keyboards, the user has consented to runtime discovery of exactly those devices.

config:

{
  "keyboard_device_names": [
    "AT Translated Set 2 keyboard",
    "SONiX USB Keyboard"
  ]
}

self-grab prevention: both discovery paths skip any device whose name contains "hyprwhspr". grabbing our own UInput virtual keyboard creates a feedback loop (physical → virtual → re-grab) that locks out all input. relevant on in-process restart when a stale virtual-keyboard node may linger briefly.

cli improvements to hyprwhspr keyboard list:

• [ALLOWED] / [VIRTUAL] markers alongside [SELECTED]
• when auto-discover is active, prints a ready-to-paste allowlist snippet using a real device name from the system
• when an allowlist is set, warns about entries that don't match any present device (catches typos vs. just-unplugged)
• drops the grab()/ungrab() accessibility test in get_available_keyboards(); it failed on devices the running service already grabbed, hiding the primary keyboard from its own cli

graceful degradation: pyudev missing → observer doesn't start, allowlist still filters startup discovery. priority between single-device and allowlist config: selected_device_name > selected_device_path > keyboard_device_names > auto-discover. consistent between startup and hotplug paths.

commits (each self-contained and bisect-safe):

1. feat: add keyboard_device_names allowlist — config, schema, main.py threading, startup filter
2. feat: auto-detect hotplugged keyboards via pyudev — monitor, hotplug path, self-grab filter, start/stop wiring, gated on the allowlist from hypewhspr : No microphone available #1
3. feat(cli): show allowlist status in keyboard list — markers, guidance, drop stale test-grab

tested locally on an arch laptop across a dock cycle: external keyboard attaches in ~1s of plug-in, triathlon mouse correctly filtered, no lockups observed.

[goodroot]

Oh dang, this is really interesting. I'll give this a review shortly. Thank you very much for taking the time to put up the pull request.

[goodroot]

Thanks again.

I will bump the AUR version for the main package in the next day or so after I sprint things locally to be sure there's no regressions. This is just tradition.

For now, it's available within the hyprwhspr-git AUR package and will also in the manual install method for everyone else.

[mmacpherson]

Thanks very much for the quick review @goodroot . Very much appreciate your work on this package; cheers!