Add Keychron RGB handler to the theme keyboard pipeline

[ueltyx]

Summary

Adds Keychron RGB support to the existing keyboard.rgb theme pipeline, following the omarchy-theme-set-keyboard-asus-rog / -f16 handler pattern exactly.

Keychron's own firmware (V/Q/K "Ultra" and "Max" series, protocol v11+) implements the VIA raw-HID protocol on a vendor config channel (USB usage page 0xFF60, usage 0x61). It is the same lighting command set the Framework 16 handler already speaks via qmk_hid: solid effect ([7,3,2,1]), HSV color ([7,3,4,h,s]), NVRAM save ([9,3]). The protocol was extracted from Keychron's own Launcher web app (WebHID client) — no firmware flashing, no reverse-engineered vendor blobs.

Changes

• bin/omarchy-keychron-rgb — transport: bash + embedded Python (stdlib only, no new packages, nothing to compile). Auto-discovers the config channel by vendor 3434 + usage-page signature and round-trip-probes it, so it works across models and connection modes (with cable and dongle both enumerated, one channel is a dead end depending on the keyboard's mode switch — the probe picks the live one).
• bin/omarchy-hw-keychron — hardware detect (USB vendor 3434), hw-* pattern.
• bin/omarchy-theme-set-keyboard-keychron — the handler; no-op without a Keychron present.
• bin/omarchy-theme-set-keyboard — dispatch entry.
• default/udev/keychron-rgb.rules + install/hardware/keychron-rgb.sh + migration — vendor-wide uaccess rule (also unblocks the official Keychron Launcher web app), mirroring framework/qmk-hid.sh.
• install/hardware/all.sh — install wiring.

Verified behavior

Tested on a Keychron V1 Ultra 8K (ZMK-based, 3434:0c10) plus Ultra-Link 8K 2.4GHz dongle (3434:d028):

• All 22 stock themes switched back-to-back; keyboard color read back over HID and matched the theme color byte-exact every time, including Tokyo Night's hand-picked keyboard.rgb (ff00ff) overriding the accent template.
• User-created themes work automatically (accent template → staged keyboard.rgb).
• Connection matrix: wired works; 2.4GHz dongle works (it tunnels the config channel; needs a radio-wake timeout, handled); Bluetooth intentionally holds the last synced color — the stock firmware exposes no config channel over BT (confirmed via the BT HID descriptor, the GATT service tree, and the Launcher client being WebHID/USB-only).
• No-op cost on non-Keychron machines: one sysfs grep; the handler exits before spawning the transport.

Testing

• ./test/cli — 116 ok, 0 failures (includes metadata lint for the new commands).
• ./test/shell — 2905 ok, 0 failures.
• End-to-end on real hardware as described above.

Transparency

This contribution was developed end-to-end with AI assistance (an agentic CLI coding assistant): protocol extraction from the Launcher bundle, tool implementation, and the automated 22-theme verification. The submitter performed all hardware verification on their machine.

One natural follow-up (not in this PR to keep it scoped): a udev RUN+ on the rule could invoke the handler on (re)plug, re-syncing the keyboard at boot and whenever it returns from wireless to wired. Happy to add if wanted.