Add Dark mode for a screen beside the bed, with every colour in one table (0.2.63)

Dark mode is a new switch under Brightness on the screen's settings page, in
the Screen settings of ESP Screens and as switch.<screen>_dark_mode in Home
Assistant, so an automation can turn it on at bedtime. The screen changes
look at once, open cards and an alert included, and keeps it after a
restart. The design stays the same: a black page, graphite cards with a
hairline, soft white text, Home Assistant's state colours where they tell
something, and pastel card colours as deeper versions of themselves.

Every colour the firmware chooses now lives in components/smart_display/
theme.h: roles with a light and a dark value, the named card colours and
Home Assistant's state colours. The board profiles give widgets colourless
shared styles that theme.h fills, so a change of look refills those styles
and draws again what code painted by state. The light look is unchanged
apart from merges below one panel step. Dark mode costs 440 bytes of static
RAM on the CYD, and the LVGL tree of the host build is 416 bytes smaller; tests
keep colours out of every other file.

Comparing a screen that switched looks with one that booted in it also
found two older bugs, now fixed: a settings switch that was on showed its
knob at the left whenever its page was drawn, and the sun card's sunlit
area turned orange after a palette change. Firmware 0.2.54.

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

AGENTS.md

@@ -49,6 +49,10 @@ physically tap; an agent cannot replace that with software coordinates.
 
 - Keep base hardware and UI in `home-like-2432s028.yaml`; personal data belongs
   in the gitignored local profiles.
+- Colours live in one table: `components/smart_display/theme.h` (firmware 0.2.54+). Every role has a
+  light and a dark value, board profiles name paints (`styles: paint_card`) instead of writing a colour,
+  and firmware code asks for a role (`theme::color(theme::INK)`). Never write a hex colour in a profile or
+  another header; docs/THEME.md is the recipe, tests/test_theme.py and tests/test_theme.cpp guard it.
 - Screen settings live in one table: `components/smart_display/settings_screen.h` draws the
   page on the screen, `SETTING_RULES` in the add-on validates the same keys. Firmware 0.2.49+
   owns them: every writer (the page, the entities in both profiles) goes through