What changed

• New optional notification that tells you when your AirPods have finished
  charging, so you know when to unplug them.
• You can set the target level (50–100%, default 100%) and choose whether it
  watches the pods, the case, or both.
• The notification clears itself once you pick up or start using the device,
  and won't nag you while you keep one pod in your ear and charge the other.
• Pro feature, configured per device in the device's Reaction settings.

Technical Context

• Charging progress is tracked by a per-profile state machine
  (IDLE/CHARGING/FIRED/DISMISSED/SUSPENDED) fed only from live BLE/AAP data —
  cached battery values never start, complete, or end a session, so a stale
  reading can't fire a false notification.
• A slot that stops charging at/above the threshold counts as "done" rather than
  "unplugged", because the firmware flips the charging flag off once a pod hits
  100%; a slot dropping below the threshold is a genuine unplug and resets the
  session.
• Brief signal loss (case closed / out of range) suspends the session instead of
  resetting it, so a momentary BLE gap mid-charge doesn't lose progress.
• Dismissal on "user is handling the device" uses worn-pod state from AAP only —
  BLE ear-detection bits are phantom for pods resting in the case — plus a lid
  change matched against a short rolling window, because the worn-pod/in-case
  advertisement pair makes the lid alternate OPEN/NOT_IN_CASE every frame and a
  single-frame baseline would dismiss itself.
• Scope is normalized to pods-only on case-less models (AirPods Max) so a restored
  profile can't get stuck waiting on a battery slot that doesn't exist.

Review checklist

• State machine covered by ChargingSessionStateMachineTest (35 cases)
• Phantom in-case ear detection gated to AAP (ChargingActivityMapperTest)
• New profile fields decode with defaults (AppleDeviceProfileSerializationTest)

Closes #575