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>

packages/boards/guition-4848s040.yaml

@@ -371,9 +371,11 @@ api:
 
 # Camera images (firmware 0.2.57+): ESP Screen Manager serves each image already sized for this screen, as an uncompressed
 # BMP on its own port on the LAN (screen_manager/app/camera_feed.py). ESPHome decodes a BMP piece by piece as it arrives,
-# 4 KB per loop, where a JPEG of the full screen held the loop for 0.6 s; touch and drawing keep their turn. One image full
-# screen and one in an alert's frame; runtime_tiles.h decides when they load and frees them when they close. Plain HTTP
-# on the LAN, no certificates.
+# one `buffer_size` per loop, where a JPEG of the full screen held the loop for 0.6 s; touch and drawing keep their turn.
+# 16 KB a loop (firmware 0.2.73+): the full picture came in 1.8 s instead of 2.8 s with 4 KB. Without Wi-Fi power save no
+# loop waited over 50 ms for it (with power save now and then 0.1 s, against 65 ms with 4 KB); 32 KB saved 0.3 s more but
+# held a loop 0.1 s even without power save (docs/TEST_RESULTS_0287.md). One image full screen and one in an alert's
+# frame; runtime_tiles.h decides when they load and frees them when they close. Plain HTTP on the LAN, no certificates.
 http_request:
   timeout: 4s
   verify_ssl: false
@@ -385,7 +387,7 @@ online_image:
     url: "http://127.0.0.1/camera.bmp"  # set when a camera opens
     format: BMP
     type: RGB565
-    buffer_size: 4096
+    buffer_size: 16384
     on_download_finished:
       - lambda: 'runtime_tiles::camera_loaded(false, cached);'
     on_error:
@@ -394,7 +396,7 @@ online_image:
     url: "http://127.0.0.1/camera.bmp"  # set when an alert brings an image
     format: BMP
     type: RGB565
-    buffer_size: 4096
+    buffer_size: 16384
     on_download_finished:
       - lambda: 'runtime_tiles::camera_loaded(true, cached);'
     on_error:
@@ -574,6 +576,7 @@ lvgl:
                 widgets:
                   # The alert's camera image (firmware 0.2.57+) across the top of the card, shown when the app announced
                   # one; a tap opens the camera full screen over the alert. runtime_tiles.h puts the image in it.
+                  # Rounded like the alert card itself (firmware 0.2.73+); the image takes this radius (camera_loaded).
                   - obj:
                       id: alert_image_frame
                       x: ${ALERT_IMAGE_INSET}
@@ -583,7 +586,7 @@ lvgl:
                       hidden: true
                       styles: paint_camera
                       bg_opa: COVER
-                      radius: 0
+                      radius: 18
                       border_width: 0
                       shadow_width: 0
                       pad_all: 0