v1.5.0 - Clean Bluetooth release on every Home Assistant shutdown

Fluval BLE v1.5.0

v1.5.0 makes every Home Assistant restart let go of the Fluval light's
Bluetooth connection cleanly, so a restart no longer leaves the light stuck on
a "ghost" connection.

Changed

• The Bluetooth link is now released automatically when Home Assistant shuts
  down - from the restart menu, an update, or anything else that stops Home
  Assistant. Before this, only running the fluvalble.release_link action
  first (the safe_restart script) avoided the stuck-light problem.

  It happens at the earliest point of shutdown, while Bluetooth and the ESPHome
  proxies are still running, and covers both cases: a link held open on purpose
  (the Hold connection option) and a short-lived one opened for a schedule
  check or a command. The light and its entities stay in place - only the
  connection is dropped.

• Once shutdown has started, the integration will not open a connection again:
  health checks, keep-alive pings, reconnect attempts, and button or light
  commands are all refused. The "light unreachable" countdown and its repair are
  switched off first, so the deliberate disconnect is never reported as an
  outage.

• Releasing is limited to 8 seconds per light and can never block or break
  shutdown; a warning is logged if the disconnect does not finish in time.

Notes

fluvalble.release_link is unchanged and still works, so safe_restart can
keep calling it until you are happy the automatic path does the job. A
"Released BLE link to at shutdown" line in the Home Assistant log
confirms it ran.