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/bing_images.go

@@ -0,0 +1,123 @@
+// kafka — a privacy-respecting metasearch engine
+// Copyright (C) 2026-present metamorphosis-dev
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+package engines
+
+import (
+	"context"
+	"encoding/xml"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"github.com/metamorphosis-dev/kafka/internal/contracts"
+)
+
+// BingImagesEngine searches Bing Images via their public RSS endpoint.
+type BingImagesEngine struct {
+	client *http.Client
+}
+
+func (e *BingImagesEngine) Name() string { return "bing_images" }
+
+func (e *BingImagesEngine) Search(ctx context.Context, req contracts.SearchRequest) (contracts.SearchResponse, error) {
+	if e == nil || e.client == nil {
+		return contracts.SearchResponse{}, errors.New("bing_images engine not initialized")
+	}
+	q := strings.TrimSpace(req.Query)
+	if q == "" {
+		return contracts.SearchResponse{Query: req.Query}, nil
+	}
+
+	offset := (req.Pageno - 1) * 10
+	endpoint := fmt.Sprintf(
+		"https://www.bing.com/images/search?q=%s&count=10&offset=%d&format=rss",
+		url.QueryEscape(q),
+		offset,
+	)
+
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	httpReq.Header.Set("User-Agent", "kafka/0.1 (compatible; +https://git.ashisgreat.xyz/penal-colony/kafka)")
+
+	resp, err := e.client.Do(httpReq)
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		io.Copy(io.Discard, io.LimitReader(resp.Body, 4096))
+		return contracts.SearchResponse{}, fmt.Errorf("bing_images upstream error: status %d", resp.StatusCode)
+	}
+
+	return parseBingImagesRSS(resp.Body, req.Query)
+}
+
+// parseBingImagesRSS parses Bing's RSS image search results.
+// The description field contains HTML with an <img> tag whose src is the
+// thumbnail and whose enclosing <a> tag links to the source page.
+func parseBingImagesRSS(r io.Reader, query string) (contracts.SearchResponse, error) {
+	type bingImageItem struct {
+		Title   string `xml:"title"`
+		Link    string `xml:"link"`
+		Descrip string `xml:"description"`
+	}
+
+	type rssFeed struct {
+		XMLName xml.Name `xml:"rss"`
+		Channel struct {
+			Items []bingImageItem `xml:"item"`
+		} `xml:"channel"`
+	}
+
+	var rss rssFeed
+	if err := xml.NewDecoder(r).Decode(&rss); err != nil {
+		return contracts.SearchResponse{}, fmt.Errorf("bing_images RSS parse error: %w", err)
+	}
+
+	results := make([]contracts.MainResult, 0, len(rss.Channel.Items))
+	for _, item := range rss.Channel.Items {
+		if item.Link == "" {
+			continue
+		}
+
+		// Extract thumbnail URL from the description HTML.
+		thumbnail := extractImgSrc(item.Descrip)
+		content := stripHTML(item.Descrip)
+
+		linkPtr := item.Link
+		results = append(results, contracts.MainResult{
+			Template:  "images",
+			Title:     item.Title,
+			Content:   content,
+			URL:       &linkPtr,
+			Thumbnail: thumbnail,
+			Engine:    "bing_images",
+			Score:     0,
+			Category:  "images",
+			Engines:   []string{"bing_images"},
+		})
+	}
+
+	return contracts.SearchResponse{
+		Query:               query,
+		NumberOfResults:    len(results),
+		Results:             results,
+		Answers:             []map[string]any{},
+		Corrections:         []string{},
+		Infoboxes:           []map[string]any{},
+		Suggestions:         []string{},
+		UnresponsiveEngines: [][2]string{},
+	}, nil
+}