Icons: small images of their own size for pages

Bitmaps that only pages use (backgrounds, images by state) are now icons:
own width and height, stored in /icons, not in the page lists or the Home
Assistant dropdowns. Page backgrounds and image elements use icons or
bitmaps; the renderer gets icons expanded at the top left, so pages look
the same. Web UI: Icons tab with an editor, Make icon / Make bitmap, Save
as icon on the Draw tab, icons in the backup.

A one-time migration in time-boxed steps moves the uploaded bitmaps that
only pages use, after the new firmware is marked good.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/home-assistant.md

@@ -57,7 +57,7 @@ Assistant's Plex and Tautulli integrations, no extra firmware:
 
 - `sensor.mangavalkserver` (Plex): how many are watching.
 - `sensor.{plex_user}_state` (Tautulli, per user): `playing`, `paused`, ... chooses the icon
-  (bitmaps `plex playing`, `plex paused`, `plex buffering`).
+  (icons `plex playing`, `plex paused`, `plex buffering`).
 - `sensor.{plex_user}_full_title` and `sensor.{plex_user}_progress` (Tautulli, per user):
   the title and the progress bar. Home Assistant creates these disabled: enable them on
   the Tautulli user's device in Home Assistant.