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>

config/config.exs

@@ -68,13 +68,6 @@ config :tailwind,
       --output=priv/static/assets/css/app.css
     ),
     cd: Path.expand("..", __DIR__)
-  ],
-  simpleshop_theme_shop: [
-    args: ~w(
-      --input=assets/css/app-shop.css
-      --output=priv/static/assets/css/app-shop.css
-    ),
-    cd: Path.expand("..", __DIR__)
   ]
 
 # Configures Elixir's Logger