fix(prefs): persist favicon choice and apply to HTML results

- Save favicon cookie on POST /preferences; reflect selection in template
- Add getFaviconService helper; pass favicon service into FromResponse
- Compute ResultView.FaviconIconURL (none/google/duckduckgo/self proxy)
- Update result_item and video_item templates; add httpapi/views tests

Made-with: Cursor

internal/views/templates/video_item.html

@@ -12,6 +12,9 @@
       <a href="{{.URL}}" target="_blank" rel="noopener noreferrer">{{.SafeTitle}}</a>
     </div>
     <div class="result_url">
+      {{if .FaviconIconURL}}
+      <img class="result-favicon" src="{{.FaviconIconURL}}" alt="" loading="lazy" width="14" height="14">
+      {{end}}
       {{if .URL}}
       <a href="{{.URL}}" target="_blank" rel="noopener noreferrer">{{.URL}}</a>
       {{end}}