feat: Wikidata engine and Wikipedia knowledge infobox

- Add wikidata engine (wbsearchentities), tests, factory/planner/config
- Wikipedia REST summary: infobox from extract, thumbnail, article URL
- InfoboxView URL; render infobox list in results_inner + base styles
- Preferences Wikidata toggle; engine badge color for wikidata

Made-with: Cursor

internal/views/templates/preferences.html

@@ -40,6 +40,10 @@
           <input type="checkbox" name="engine" value="wikipedia" checked>
           <span>Wikipedia</span>
         </label>
+        <label class="engine-toggle">
+          <input type="checkbox" name="engine" value="wikidata" checked>
+          <span>Wikidata</span>
+        </label>
         <label class="engine-toggle">
           <input type="checkbox" name="engine" value="github">
           <span>GitHub</span>