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>

mix.exs

@@ -99,13 +99,11 @@ defmodule SimpleshopTheme.MixProject do
       "assets.build": [
         "compile",
         "tailwind simpleshop_theme",
-        "tailwind simpleshop_theme_shop",
         "esbuild simpleshop_theme",
         "esbuild simpleshop_theme_shop_css"
       ],
       "assets.deploy": [
         "tailwind simpleshop_theme --minify",
-        "tailwind simpleshop_theme_shop --minify",
         "esbuild simpleshop_theme --minify",
         "esbuild simpleshop_theme_shop_css --minify",
         "phx.digest"