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/engines/factory.go

@@ -50,6 +50,7 @@ func NewDefaultPortedEngines(client *http.Client, cfg *config.Config) map[string
 
 	return map[string]Engine{
 		"wikipedia": &WikipediaEngine{client: client},
+		"wikidata":  &WikidataEngine{client: client},
 		"arxiv":     &ArxivEngine{client: client},
 		"crossref":  &CrossrefEngine{client: client},
 		"braveapi": &BraveAPIEngine{