replace --color-* with --t-* tokens, delete bridge and .preview-frame

Phase 4: admin components and utilities now reference --t-* theme
tokens directly. Status colour tokens added to theme-semantic.css.
Bridge file (admin/themes.css) deleted.

Phase 5: removed duplicated .preview-frame CSS block (~160 lines).
Admin components and icons wrapped in @layer admin. Layer order
updated in admin_root to include admin layer.

Phase 6: added prefers-reduced-motion support (zeroes all durations
and disables animations). Migrated physical properties to logical
equivalents (text-align start/end, margin-inline, padding-inline,
inset-inline-end) across shop and admin CSS.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/berrypod_web/live/admin/theme/index.html.heex

@@ -1147,7 +1147,7 @@
         
 <!-- Preview Frame -->
         <div
-          class="themed preview-frame bg-white overflow-auto flex-1 rounded-b-lg border border-t-0 border-base-content/20"
+          class="themed overflow-auto flex-1 rounded-b-lg border border-t-0 border-base-content/20"
           data-mood={@theme_settings.mood}
           data-typography={@theme_settings.typography}
           data-shape={@theme_settings.shape}