split contrast gate + ship -hc theme variants (T-114, T-118)

The expanded canonicalPairs from T-114 (muted text, status chips,
syntax tokens on the code-block surface, panel focus border) made the
four named themes fail WCAG-AA. Retuning their palettes to pass would
have changed the look users picked them for, so the gate is split
instead.

`canonicalPairs` shrinks back to the baseline every named theme passes;
the new `extendedPairs` carries the stricter set and only runs against
themes whose name ends `-hc` or `-cb`. Sibling files (`clide-hc`,
`midnight-hc`, `paper-hc`, `terminal-hc`) ship today; the policy lives
in D-69 with a back-ref from D-22.

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

lib/test_app.dart

@@ -246,6 +246,10 @@ class _ClideTestAppState extends State<ClideTestApp> {
         'lib/kernel/src/theme/themes/midnight.yaml',
         'lib/kernel/src/theme/themes/paper.yaml',
         'lib/kernel/src/theme/themes/terminal.yaml',
+        'lib/kernel/src/theme/themes/clide-hc.yaml',
+        'lib/kernel/src/theme/themes/midnight-hc.yaml',
+        'lib/kernel/src/theme/themes/paper-hc.yaml',
+        'lib/kernel/src/theme/themes/terminal-hc.yaml',
       ];
       for (final p in paths) {
         final name = p.split('/').last.replaceAll('.yaml', '');