Dark/bright: Auto (Android's dark theme), Dark or Bright, kept across restarts

Settings has a segmented Auto / Dark / Bright. Auto follows platformBrightness, so
Android's schedule too. The Dash's quick button holds the other variant; a long press
is auto again. The mode is kept with shared_preferences.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/README.md

@@ -16,7 +16,7 @@ pirate-station-aide's (main views, then the rarely used ones grouped as Tools).
 | `pages/` | One file per view: `dash`, `signals` (values and raw traffic), `checklist` (Captures), `camera`, `link_test`, `settings` |
 | `actions/` | Things done from anywhere, as dialogs and sheets: `marks` (free-form mark), `orin_power` (power off / reboot), `server_url` (gateway address) |
 | `link/` | Talking to the Orin: `boundary` (the protocol client), `net` (binding to the USB link), `reading` (one signal's state as a display needs it) |
-| `theme/` | `palette.dart`: the palette roles and `hudFont` |
+| `theme/` | `palette.dart`: the palette roles, `hudFont`, and `Themes` (which variant shows: auto or held, kept across restarts) |
 | `widgets/` | Reusable display widgets, one per file, each fed values, never the boundary (`link_status` takes it whole: it shows the link) |
 
 ## Widgets
@@ -40,6 +40,9 @@ pirate-station-aide's (main views, then the rarely used ones grouped as Tools).
   and the state gradient `good` → `caution` → `alarm`; plus the derived `surface` (raised bars) and
   `onFill(colour)` (text on a fill). No widget names a colour. Themes are JSON in `assets/themes/`, `rei` by
   default; smart-serow's four-key files still load (their `highlight` is `alarm`).
+- **Dark or bright.** `Themes.mode` is `auto` (Android's dark theme, schedule included), `dark` or
+  `bright`, chosen in Settings and kept across restarts. The Dash's quick button holds the other variant;
+  a long press there is auto again.
 - **Cosmetic fonts are opt-in.** A widget that wants the HUD face names `fontFamily: hudFont` in its own
   `TextStyle`; everything else keeps the basic font, which covers CJK where DIN 1451 does not.
 - **Missing is a state** (app guideline 2): a widget given no value draws "—" or subdued, never an error.