test/hil: add stm32u083nucleo to pool and expose ~/bin on remote PATH

Add stm32u083nucleo to the active boards in tinyusb.json, flashed via the
stlink flasher (onboard ST-Link + STM32CubeProgrammer); ci's openocd build
has no STM32U0 flash driver. STM32_Programmer_CLI lives in ~/bin on ci,
which the remote `bash -s` shell in hil_ci.sh did not have on PATH, so add
$HOME/bin to its PATH export (matching the GHA runner .path). Verified
remote: 13/13 device tests pass on ci.lan.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>