v0.4.0b3

Beta. Fixes the preset flow's discoverability.

• The charger-wide Preset name field and the per-channel save preset
  buttons are replaced by one field per channel: Channel X save preset as.
  Type a name, press enter — the staged program is saved and the field clears.
  It now sits next to that channel's preset select instead of forty rows
  away in the alphabetically sorted configuration list.
• The entities it replaces are removed from the registry automatically.

Everything from 0.4.0b1/b2 is unchanged: storage runs report
charging/discharging, the options and reauth dialogs load, entered values are
kept across program changes and disconnects, and the config-side entities load
even when the charger is out of Bluetooth range.