0.5.11 — find out why a heater test did nothing

A heater reported a successful test and did not switch on — no LED on the MOSFET, nothing on a thermal camera. The test could say it had driven the pin; it could not say whether anything real was behind it.

Fixed

The dew heater's libraries were never installed. They live in an optional [dewheater] extra, install.sh installs [zwo], and the updater installed plain . — so nothing installed them. Sensor detection is raw smbus2 and works without them, which is why the card said "sensor found" on a camera that could never produce a single reading.

Both now install [zwo,dewheater], with tests asserting the installer and updater agree, and that every declared extra is installed by somebody.

Added

• The test reports which gpiozero backend drove the pin. gpiozero will happily drive a mock and report success, which from the outside is identical to working hardware. On a Pi 5 the backend must be lgpio.
• A failed sensor read now says why instead of silently returning no temperature.
• /api/dewheater/diagnostics — which libraries import, which address answers, which backend is in play, in one place.

None of this proves any wiring is correct. It removes the software from the list of suspects.