feat: add image search with Bing, DuckDuckGo, and Qwant engines

Three new image search engines:
- bing_images: Bing Images via RSS endpoint
- ddg_images: DuckDuckGo Images via VQD API
- qwant_images: Qwant Images via v3 search API

Frontend:
- Image grid layout with responsive columns
- image_item template with thumbnail, title, and source metadata
- Hover animations and lazy loading
- Grid activates automatically when category=images

Backend:
- category=images routes to image engines via planner
- Image engines registered in factory and engine allowlist
- extractImgSrc helper for parsing thumbnail URLs from HTML
- IsImageSearch flag on PageData for template layout switching

internal/views/views.go

@@ -52,6 +52,7 @@ type PageData struct {
 	UnresponsiveEngines [][2]string
 	PageNumbers         []PageNumber
 	ShowHeader          bool
+	IsImageSearch       bool
 	// New fields for three-column layout
 	Categories         []string
 	CategoryIcons     map[string]string
@@ -106,13 +107,13 @@ func init() {
 	}
 
 	tmplFull = template.Must(template.New("").Funcs(funcMap).ParseFS(tmplFS,
-		"base.html", "results.html", "results_inner.html", "result_item.html", "video_item.html",
+		"base.html", "results.html", "results_inner.html", "result_item.html", "video_item.html", "image_item.html",
 	))
 	tmplIndex = template.Must(template.New("").Funcs(funcMap).ParseFS(tmplFS,
 		"base.html", "index.html",
 	))
 	tmplFragment = template.Must(template.New("").Funcs(funcMap).ParseFS(tmplFS,
-		"results.html", "results_inner.html", "result_item.html", "video_item.html",
+		"results.html", "results_inner.html", "result_item.html", "video_item.html", "image_item.html",
 	))
 	tmplPreferences = template.Must(template.New("").Funcs(funcMap).ParseFS(tmplFS,
 		"base.html", "preferences.html",
@@ -168,6 +169,7 @@ func FromResponse(resp contracts.SearchResponse, query string, pageno int, activ
 			"weather":  "🌤️",
 		},
 		ActiveCategory: activeCategory,
+		IsImageSearch:  activeCategory == "images",
 
 		// Time filters
 		TimeFilters: []FilterOption{