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>

components/smart_display/theme.h

@@ -76,7 +76,8 @@ enum Role : uint8_t {
   // ---- a camera image: dark in both looks, like a photo viewer (firmware 0.2.57+)
   CAMERA_PAGE,          // behind the image full screen and in the alert's image frame
   CAMERA_INK,           // the camera's name over the image
-  CAMERA_NOTE,          // "Loading image", "No image from this camera"
+  CAMERA_NOTE,          // "No image from this camera"
+  CAMERA_TRACK,         // the ring of the spinner while the first image loads (firmware 0.2.73+)
   // ---- the CYD's touch calibration: dark in both looks, a yellow crosshair
   CALIBRATION_PAGE,
   CALIBRATION_INK,
@@ -144,6 +145,7 @@ inline constexpr Pair ROLES[ROLE_COUNT] = {
   /* CAMERA_PAGE */              {0x000000, 0x000000},
   /* CAMERA_INK */               {0xF2F2F2, 0xDADADA},
   /* CAMERA_NOTE */              {0x9E9E9E, 0x8A8A8A},
+  /* CAMERA_TRACK */             {0x393D42, 0x393D42},
   /* CALIBRATION_PAGE */         {0x101820, 0x101820},
   /* CALIBRATION_INK */          {0xFFFFFF, 0xFFFFFF},
   /* CALIBRATION_MARK */         {0xFFD34D, 0xFFD34D},