v1.21.0 — custom entity tiles

Tiles could only come from the built-in catalogue, which only covers what an Ecowitt station reports. Now a tile can be any entity at all.

Click Custom entity in the weather card editor and pick one from the entity picker, or write it directly:

metrics:
  - hum_out
  - entity: sensor.rainwater_tank_level
  - entity: sensor.pool_temperature
    name: Pool

A custom tile takes its label, icon and decimal places from the entity itself, so an entity id alone is a complete entry. Icons fall back through the entity's own icon, then its device class, then a generic gauge. Give it a name to override the label — often worth it, since Home Assistant friendly names are long enough to truncate. Custom and catalogue tiles mix freely and reorder together.

Two bugs surfaced only by driving the editor in a browser, which the unit tests can't do because they never construct it: the entity picker was declared in the wrong row builder, so opening the editor threw and it silently failed to mount; and a tile with no entity yet — the state of every custom tile the moment it is added — was being discarded as malformed, so the row vanished before there was anywhere to pick anything.