Show a spinner while a screen starts and while a camera loads, bring a camera's first picture sooner, and round the alert's camera picture (0.2.87)

Starting screen: until the first layout, render() keeps the status text
("Connecting to Home Assistant", "Waiting for ESP Screens") and a spinner
as one block in the middle of the page; the first layout deletes both.
The room label stays empty meanwhile, and ROOM_NAME defaults to "".

Camera: the full screen shows a spinner instead of "Loading image". The
screen asks when the camera opens and loads a link as soon as it comes
(camera_load, never under a finger) instead of waiting for the 250 ms
tick twice, and online_image reads 16 KB per loop instead of 4 KB. On the
bench Guition with the EZVIZ camera: cold 5.8 -> 4.55 s, warm 3.4 -> 2.06 s.

Alert picture: the image takes the frame's radius (18, the alert card's);
LVGL's software renderer clips it row by row, without a layer.

One spinner_create() makes the busy sheet's, the starting screen's and the
camera's spinner; theme role CAMERA_TRACK colours the camera's ring. The
README gets a row of camera pictures; docs/CAMERA.md, RELEASING.md and
TEST_RESULTS_0287.md describe the measurements.

Checked with tools/check.sh (473 Python tests, 19/19 C++, editor) and
--firmware: CYD 1,678,816 B (91.5 %, +1,312 B), Guition 2,055,280 B
(25.3 %). Host renders of both boards in both looks; four OTA builds on
the bench Guition Wallbox, which runs this firmware.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README_EXTENDED.md

@@ -117,6 +117,11 @@ on the screen itself, and how updates work.
   off shows a power key. A Guition fetches the cover through ESP Screens, like a camera picture
   ([docs/CAMERA.md](docs/CAMERA.md)); the CYD shows the player's icon in its place. A media tile of
   size **Full page** is the same card on the page, with the keys and the volume working on the tile.
+- **Cameras** on a Guition (app 0.2.66 / firmware 0.2.57): a `camera.*` entity, or an `image.*` one such
+  as a doorbell's last ring, is a tile like any other. A tap opens the picture full screen, refreshed every
+  four seconds, with the round back key; standby and **Back to page 1** close it. The same camera can bring its
+  picture to an alert ([With a camera picture](#with-a-camera-picture)). The CYD has no memory for pictures and
+  the editor doesn't offer it camera tiles. How the picture travels: [docs/CAMERA.md](docs/CAMERA.md).
 - **History card** for sensors, numbers, binary sensors, people, and switches, the way Home
   Assistant shows history: a line with an axis in round steps and clock times for numbers,
   with the highest and lowest moment, and a timeline with the time in each state for on/off,
@@ -297,6 +302,10 @@ actions:
       camera: camera.front_door
 ```
 
+<p align="center">
+  <img src="docs/images/guition-camera-tiles.png" width="41%" alt="Cameras as tiles on the Guition: the front door camera, the garden camera live, the doorbell's last ring, next to the door, the porch light and the garage door">
+</p>
+
 A camera or image entity also works as a **tile** on a Guition: a tap opens it full screen, refreshed
 every four seconds. How the image travels (port 8098 of the app, no token on the screen) is in
 [docs/CAMERA.md](docs/CAMERA.md).