feat: add comprehensive social platform icons using Simple Icons

Add 24 social platform icons from Simple Icons (MIT licensed):
- Commercial/Creative: instagram, pinterest, tiktok, facebook, twitter,
  youtube, patreon, kofi, etsy, gumroad, bandcamp
- Open Web/Federated: mastodon, pixelfed, bluesky, peertube, lemmy, matrix
- Developer/Hacker: github, gitlab, codeberg, sourcehut
- Communication: discord, telegram, signal
- Other: substack, rss, website

Also:
- Redesign social_links_card to single card with compact flex-wrap layout
- Remove redundant response_time text (hero already says "get back to you")

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/simpleshop_theme_web/components/page_templates/contact.html.heex

@@ -15,7 +15,7 @@
     />
 
     <div class="grid gap-8 md:grid-cols-2 mb-12">
-      <.contact_form email="hello@example.com" response_time="We typically respond within 24 hours" />
+      <.contact_form email="hello@example.com" />
 
       <div class="space-y-6">
         <.order_tracking_card />