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>

screen_manager/app/core.py

@@ -37,7 +37,7 @@ WEEKDAYS = ['Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa', 'Su']
 REPO = 'https://github.com/MaxGramser/homeassistant_espscreen'
 REFS = {'cyd': 'main', 'guition': 'main'}
 # Firmware shipped with this app release; screens below it get an update offer.
-FIRMWARE_VERSION = '0.2.72'
+FIRMWARE_VERSION = '0.2.73'
 # The Auto standby switch a screen offers Home Assistant automations.
 AUTO_STANDBY_MIN_FIRMWARE = '0.2.41'
 # The settings page the screen opens itself, and the screen.settings tile that opens it.