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/ddg_images.go

@@ -0,0 +1,207 @@
+// 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/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+
+	"github.com/metamorphosis-dev/kafka/internal/contracts"
+)
+
+// DuckDuckGoImagesEngine searches DuckDuckGo Images via their vql API.
+type DuckDuckGoImagesEngine struct {
+	client *http.Client
+}
+
+func (e *DuckDuckGoImagesEngine) Name() string { return "ddg_images" }
+
+func (e *DuckDuckGoImagesEngine) Search(ctx context.Context, req contracts.SearchRequest) (contracts.SearchResponse, error) {
+	if e == nil || e.client == nil {
+		return contracts.SearchResponse{}, errors.New("ddg_images engine not initialized")
+	}
+	q := strings.TrimSpace(req.Query)
+	if q == "" {
+		return contracts.SearchResponse{Query: req.Query}, nil
+	}
+
+	// Step 1: Get a VQD token from the initial search page.
+	vqd, err := e.getVQD(ctx, q)
+	if err != nil {
+		return contracts.SearchResponse{
+			Query:               req.Query,
+			UnresponsiveEngines: [][2]string{{"ddg_images", "vqd_fetch_failed"}},
+			Results:             []contracts.MainResult{},
+			Answers:             []map[string]any{},
+			Corrections:         []string{},
+			Infoboxes:           []map[string]any{},
+			Suggestions:         []string{},
+		}, nil
+	}
+
+	// Step 2: Fetch image results using the VQD token.
+	endpoint := fmt.Sprintf(
+		"https://duckduckgo.com/i.js?q=%s&kl=wt-wt&l=wt-wt&p=1&s=%d&vqd=%s",
+		url.QueryEscape(q),
+		(req.Pageno-1)*50,
+		url.QueryEscape(vqd),
+	)
+
+	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)")
+	httpReq.Header.Set("Referer", "https://duckduckgo.com/")
+
+	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, 16*1024))
+		return contracts.SearchResponse{}, fmt.Errorf("ddg_images upstream error: status %d", resp.StatusCode)
+	}
+
+	body, err := io.ReadAll(io.LimitReader(resp.Body, 2*1024*1024))
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+
+	return parseDDGImages(body, req.Query)
+}
+
+// getVQD fetches a VQD token from DuckDuckGo's search page.
+func (e *DuckDuckGoImagesEngine) getVQD(ctx context.Context, query string) (string, error) {
+	endpoint := "https://duckduckgo.com/?q=" + url.QueryEscape(query)
+
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		return "", 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 "", err
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(io.LimitReader(resp.Body, 512*1024))
+	if err != nil {
+		return "", err
+	}
+
+	// Extract VQD from the HTML: vqd='...'
+	vqd := extractVQD(string(body))
+	if vqd == "" {
+		return "", fmt.Errorf("vqd token not found in response")
+	}
+	return vqd, nil
+}
+
+// extractVQD extracts the VQD token from DuckDuckGo's HTML response.
+func extractVQD(html string) string {
+	// Look for: vqd='...' or vqd="..."
+	for _, prefix := range []string{"vqd='", `vqd="`} {
+		idx := strings.Index(html, prefix)
+		if idx == -1 {
+			continue
+		}
+		start := idx + len(prefix)
+		end := start
+		for end < len(html) && html[end] != '\'' && html[end] != '"' {
+			end++
+		}
+		if end > start {
+			return html[start:end]
+		}
+	}
+	return ""
+}
+
+// ddgImageResult represents a single image result from DDG's JSON API.
+type ddgImageResult struct {
+	Title   string `json:"title"`
+	URL     string `json:"url"`
+	Thumbnail string `json:"thumbnail"`
+	Image   string `json:"image"`
+	Width   int    `json:"width"`
+	Height  int    `json:"height"`
+	Source  string `json:"source"`
+}
+
+func parseDDGImages(body []byte, query string) (contracts.SearchResponse, error) {
+	var results struct {
+		Results []ddgImageResult `json:"results"`
+	}
+
+	if err := json.Unmarshal(body, &results); err != nil {
+		return contracts.SearchResponse{}, fmt.Errorf("ddg_images JSON parse error: %w", err)
+	}
+
+	out := make([]contracts.MainResult, 0, len(results.Results))
+	for _, img := range results.Results {
+		if img.URL == "" {
+			continue
+		}
+
+		// Prefer the full image URL as thumbnail, fall back to the thumbnail field.
+		thumb := img.Image
+		if thumb == "" {
+			thumb = img.Thumbnail
+		}
+
+		// Build a simple content string showing dimensions.
+		content := ""
+		if img.Width > 0 && img.Height > 0 {
+			content = strconv.Itoa(img.Width) + " × " + strconv.Itoa(img.Height)
+		}
+		if img.Source != "" {
+			if content != "" {
+				content += " — " + img.Source
+			} else {
+				content = img.Source
+			}
+		}
+
+		urlPtr := img.URL
+		out = append(out, contracts.MainResult{
+			Template:  "images",
+			Title:     img.Title,
+			Content:   content,
+			URL:       &urlPtr,
+			Thumbnail: thumb,
+			Engine:    "ddg_images",
+			Score:     0,
+			Category:  "images",
+			Engines:   []string{"ddg_images"},
+		})
+	}
+
+	return contracts.SearchResponse{
+		Query:               query,
+		NumberOfResults:    len(out),
+		Results:             out,
+		Answers:             []map[string]any{},
+		Corrections:         []string{},
+		Infoboxes:           []map[string]any{},
+		Suggestions:         []string{},
+		UnresponsiveEngines: [][2]string{},
+	}, nil
+}