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>

lib/simpleshop_theme_web/components/layouts/shop_root.html.heex

@@ -23,7 +23,6 @@
     <style>
       @layer properties, reset, primitives, tokens, theme, base, components, layout, utilities, overrides;
     </style>
-    <link phx-track-static rel="stylesheet" href={~p"/assets/css/app-shop.css"} />
     <link phx-track-static rel="stylesheet" href={~p"/assets/css/shop.css"} />
     <script defer phx-track-static src={~p"/assets/js/app.js"}>
     </script>