replace Tailwind in content + collection, remove shop Tailwind entirely (Phase 5c)

- Replace all Tailwind utilities in content.ex and collection.ex with
  semantic CSS classes (content body, contact form, cards, reviews, etc.)
- Delete app-shop.css (Tailwind shop entry point)
- Remove shop Tailwind config from config.exs, dev.exs, mix.exs
- Remove shop Tailwind stylesheet link from shop_root.html.heex
- Add collection filter bar, empty state, and select dropdown styles
- Fix filter pill sizing (use theme font vars instead of hardcoded rem)
- Fix active pill contrast (tinted accent background + dark accent text)
- Fix --t-text-on-accent fallback for pill legibility
- Add padding/font-size to .themed-select

Shop pages now use zero Tailwind. Admin Tailwind remains for Phase 6.

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

assets/css/theme-layer2-attributes.css

@@ -263,6 +263,9 @@
     color: var(--t-text-primary);
     border: 1px solid var(--t-border-default);
     border-radius: var(--t-radius-input);
+    padding: 0.375rem 0.75rem;
+    font-size: var(--t-text-small);
+    font-family: var(--t-font-body);
 
     &:focus {
       outline: none;
@@ -293,8 +296,7 @@
   }
 }
 
-/* Shop nav display - hidden on mobile, flex on md+ (via Tailwind classes in component) */
-/* Note: Removed explicit display:flex here as it overrides Tailwind's hidden class */
+/* Shop nav display - handled by components.css (hidden on mobile, flex on md+) */
 
 /* =============================================
    STANDALONE COMPONENTS (Context-independent)