v0.3.10 - Standby button (remote power-off)

Added

Standby button - power the machine off remotely. ⏻

The power command family (0x84 0x0f) has a standby payload (params 01 01, CRC 0x0041) first reported on an Eletta Explore by @TischenkoArseny (#1) and validated live on the reference PrimaDonna Soul - the machine powers off exactly as with the physical button.

The official Coffee Link app exposes no power-off control, so the frame is always synthesized:

• Soul (DL-millcore): works out of the box.
• Eletta Explore (and other learn-and-replay models): the per-device signature is appended from any already-learned frame (e.g. the wake frame) - so once the one-time Wake teach step is done, Standby works too. Until then a best-effort unsigned frame is sent with a clear log message.

51 tests pass. Wake / beverage paths untouched.