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/dev.exs

@@ -27,8 +27,7 @@ config :simpleshop_theme, SimpleshopThemeWeb.Endpoint,
     esbuild: {Esbuild, :install_and_run, [:simpleshop_theme, ~w(--sourcemap=inline --watch)]},
     esbuild_shop_css:
       {Esbuild, :install_and_run, [:simpleshop_theme_shop_css, ~w(--sourcemap=inline --watch)]},
-    tailwind: {Tailwind, :install_and_run, [:simpleshop_theme, ~w(--watch)]},
-    tailwind_shop: {Tailwind, :install_and_run, [:simpleshop_theme_shop, ~w(--watch)]}
+    tailwind: {Tailwind, :install_and_run, [:simpleshop_theme, ~w(--watch)]}
   ]
 
 # ## SSL Support