feat: complete UI redesign — modern, clean search interface

- New CSS: complete design system with CSS variables, modern color palette
- Homepage: full-viewport hero with centered search, logo, tagline
- Result cards: rounded, shadowed, with favicons via Google Favicon API
- Layout: sidebar + results grid, responsive
- Typography: proper font stack, variable weights
- Settings panel: polished popover with animations
- Autocomplete: modern dropdown with keyboard nav
- Dark mode: full color palette via data-theme attribute
- Favicon: clean search icon SVG

internal/views/templates/video_item.html

@@ -8,15 +8,15 @@
   </div>
   {{end}}
   <div class="result_content_wrapper">
-    <h3 class="result_header">
+    <div class="result_header">
       <a href="{{.URL}}" target="_blank" rel="noopener noreferrer">{{.Title}}</a>
-    </h3>
+    </div>
+    <div class="result_url">
+      <span class="engine-badge">youtube</span>
+    </div>
     {{if .Content}}
     <p class="result_content">{{.Content}}</p>
     {{end}}
-    {{if .Engine}}
-    <div class="result_engine"><span class="engine">{{.Engine}}</span></div>
-    {{end}}
   </div>
 </article>
 {{end}}