feat: 3-column layout with centered results and right column

- results-layout: 3-column grid (1fr | min(768px,100%) | 300px) max-width 1400px, centered
- Widen center results column to 768px max
- Right column (formerly sidebar): sticky, contains knowledge panel + related searches
- Knowledge panel: Wikipedia/infobox summary with optional thumbnail
- Related searches: clickable links to refine the query
- Empty left buffer creates balanced whitespace on large screens
- Responsive: 2-col at 1000px, 1-col at 700px

internal/views/templates/results_inner.html

@@ -8,13 +8,6 @@
   {{range .Answers}}
   <div class="dialog-error">{{.}}</div>
   {{end}}
-  {{range .Infoboxes}}
-  <div class="infobox">
-    {{if .title}}<div class="title">{{.title}}</div>{{end}}
-    {{if .content}}<div>{{.content}}</div>{{end}}
-    {{if .img_src}}<img src="{{.img_src}}" alt="{{.title}}">{{end}}
-  </div>
-  {{end}}
 </div>
 {{end}}