Keep every screen's Wi-Fi awake from the shared core, so Home Assistant's messages no longer wait for the router's next beacon (0.2.88)

packages/core.yaml sets wifi: power_save_mode: none. ESPHome merges it
under the screen's own wifi: block, which keeps the network, the password
and the hotspot, and the screen's own YAML still wins on the mode. The
YAML ESP Screens writes has had the line since app 0.2.24; screens with
an older or hand-written YAML ran ESPHome's ESP32 default light, and
their messages from Home Assistant waited 76-117 ms on the bench.

esphome config on the bench screens' Device Builder YAMLs: NONE for both
without a line of their own, LIGHT when the YAML says light. The bench
Guition, flashed from its Device Builder YAML: ping 15 ms average instead
of 117 ms. tools/check.sh: 474 Python tests (a new one keeps the core's
wifi: block to this one key), 19/19 C++, editor; firmware unchanged in
size (CYD 1,678,816 B, 91.5 %; Guition 2,055,280 B), since the checkout
profiles already had the line.

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

docs/CAMERA.md

@@ -99,8 +99,9 @@ Guition it comes in about 1.8 s (2.8 s with 4 KB).
   camera's last snapshot (it keeps one for 30 s after the last load), 4.5 s when it must ask Home
   Assistant first, of which 2.4 s is the camera's own snapshot. Firmware 0.2.72 took 3.4 s and
   5.8 s. Details in docs/TEST_RESULTS_0287.md.
-- `power_save_mode: none` under `wifi:` (the YAML ESP Screens writes has it since app 0.2.24) keeps
-  the screen from waiting on its Wi-Fi now and then while an image comes in.
+- Wi-Fi without power save (firmware 0.2.74 sets `power_save_mode: none` itself) makes the screen
+  wait on its Wi-Fi less often while an image comes in: a loop held over 50 ms in one of eleven
+  opens, against five of twelve with power save.
 
 ## For developers