Dynamic color: keep card surfaces lighter than the page

In light mode surfaceContainerLow is slightly darker than the OS surface bg
maps to, so the selection bar and other cards blended into the page. Use
surfaceContainerLowest (light) / surfaceContainer (dark) for NooColors.surface.

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

.claude/context/styling.md

@@ -29,6 +29,13 @@ widgets. Key points:
   whole app in `main.dart`. When available and `useDynamicColor` is on, the
   OS-provided `ColorScheme` wins over the seed color — always thread both
   `dynamicScheme` and `useDynamicColor` through when adding a theme knob.
+  `NooColors.fromDynamicScheme` keeps `bg` on the OS `surface` but picks
+  `surface` (cards, selection bar, rows) from the container roles so it
+  stays lighter than `bg`: `surfaceContainerLowest` (white) in light,
+  `surfaceContainer` in dark. The dynamic_color package seeds the container
+  roles from the primary color rather than the OS palette, and in light mode
+  `surfaceContainerLow` is slightly *darker* than the OS `surface`, which
+  made cards blend into the page ("the selection bar has no background").
 - **Font**: Inter via `google_fonts`, applied through
   `GoogleFonts.interTextTheme(...)`. Font files ship in
   `assets/google_fonts/` (Instrument Sans, Schibsted Grotesk) and