feat(portfolio): hover overlay for all cards + mobile tap + case studies cleanup

Changes:
- Deleted 9 case studies A-I (no real URLs)
- Researched 5 real client websites (Baofuling, Lungfinler, Trainersunny, Underdog, Luadjob) and wrote accurate what_we_did
- Added mobile tap support (ontouchstart toggle + .tapped class)
- All 9 remaining portfolio cards now use hover/tap overlay for what_we_did
- Removed fabricated features from what_we_did (user-caught: ระบบขอใบเสนอราคา, ระบบนัดหมาย)

src/components/PortfolioCard.astro

@@ -18,7 +18,9 @@ interface Props {
 const { name, url, category, category_label, industry, thumbnail, description, what_we_did, result } = Astro.props;
 ---
 
-<a href={url || '#'} target="_blank" rel="noopener noreferrer" class="portfolio-card" data-category={category}>
+<a href={url || '#'} target="_blank" rel="noopener noreferrer" class="portfolio-card" data-category={category}
+   ontouchstart="this.classList.toggle('tapped')"
+   onclick="if(this.classList.contains('tapped')&&window.innerWidth<768){this.classList.remove('tapped');return false;}">
   <div class="portfolio-image">
     <img src={thumbnail} alt={name} loading="lazy" />
     <div class="portfolio-overlay">
@@ -93,7 +95,8 @@ const { name, url, category, category_label, industry, thumbnail, description, w
     transition: opacity 0.3s ease;
   }
 
-  .portfolio-card:hover .portfolio-overlay {
+  .portfolio-card:hover .portfolio-overlay,
+  .portfolio-card.tapped .portfolio-overlay {
     opacity: 1;
   }