Palette: seven roles (accent, good, caution added; highlight renamed alarm); no hard-coded colours left

background, foreground, subdued, accent (emphasis without danger), and the state
gradient good → caution → alarm; surface and onFill derived. smart-serow's
four-key themes still load (highlight = alarm; the new roles fall back).
Material's scheme follows: buttons in accent instead of the alarm colour.
Link state, mock banner, signal tiles, raw log, checklist button and marks,
camera page all take palette roles.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

lib/widgets/telltale.dart

@@ -7,7 +7,7 @@ import '../reading.dart';
 import '../theme/palette.dart';
 
 /// An on/off lamp in the boxed pattern: the label is the lamp. Lit in foreground
-/// (highlight when [warn]), dark in subdued; missing shows as a dash.
+/// (alarm when [warn]), dark in subdued; missing shows as a dash.
 class Telltale extends StatelessWidget {
   const Telltale({
     super.key,
@@ -32,7 +32,7 @@ class Telltale extends StatelessWidget {
     final missing = reading.value == null;
     final lit = reading.on && !reading.dim;
     final color = lit
-        ? (warn ? p.highlight : p.foreground)
+        ? (warn ? p.alarm : p.foreground)
         : p.subdued.withValues(alpha: missing ? 0.35 : 0.6);
     return Expanded(
       flex: flex,