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/engines/planner.go

@@ -23,7 +23,13 @@ import (
 	"github.com/metamorphosis-dev/kafka/internal/contracts"
 )
 
-var defaultPortedEngines = []string{"wikipedia", "arxiv", "crossref", "braveapi", "brave", "qwant", "duckduckgo", "github", "reddit", "bing", "google", "youtube"}
+var defaultPortedEngines = []string{
+	"wikipedia", "arxiv", "crossref", "braveapi",
+	"brave", "qwant", "duckduckgo", "github", "reddit",
+	"bing", "google", "youtube",
+	// Image engines
+	"bing_images", "ddg_images", "qwant_images",
+}
 
 type Planner struct {
 	PortedSet  map[string]bool
@@ -114,6 +120,10 @@ func inferFromCategories(categories []string) []string {
 			set["reddit"] = true
 		case "videos":
 			set["youtube"] = true
+		case "images":
+			set["bing_images"] = true
+			set["ddg_images"] = true
+			set["qwant_images"] = true
 		}
 	}
 
@@ -122,7 +132,11 @@ func inferFromCategories(categories []string) []string {
 		out = append(out, e)
 	}
 	// stable order
-	order := map[string]int{"wikipedia": 0, "braveapi": 1, "brave": 2, "qwant": 3, "duckduckgo": 4, "bing": 5, "google": 6, "arxiv": 7, "crossref": 8, "github": 9, "reddit": 10, "youtube": 11}
+	order := map[string]int{
+		"wikipedia": 0, "braveapi": 1, "brave": 2, "qwant": 3, "duckduckgo": 4, "bing": 5, "google": 6,
+		"arxiv": 7, "crossref": 8, "github": 9, "reddit": 10, "youtube": 11,
+		"bing_images": 12, "ddg_images": 13, "qwant_images": 14,
+	}
 	sortByOrder(out, order)
 	return out
 }