[garyng]

A mod-tap set from Launcher or VIA with several modifiers, such as MT(MOD_MEH, KC_CAPS), held only the lowest one. MEH sent Ctrl alone.

mod_to_zmk_keycode() returned the keycode of the first modifier bit it found and dropped the rest. Its uint8_t return type could not carry modifier flags either.

Return the first modifier's keycode with the remaining modifiers in the top byte, the same encoding as LC(LS(LALT)). ZMK treats those as explicit modifiers when the keycode is itself a modifier, so all of them are held.

Tested on a B6 Pro ANSI (PID 0x076B, keychron_b6_usn).

PR check-list

• Branch has a clean commit history
• Additional tests are included, if changing behaviors/core code that is testable.
• Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
• Pre-commit used to check formatting of files, commit messages, etc.
• Includes any necessary documentation changes.