feat: add DuckDuckGo, GitHub, Reddit, and Bing engines

- DuckDuckGo: scrapes Lite HTML endpoint for results
  - Language-aware region mapping (de→de-de, ja→jp-jp, etc.)
  - HTML parser extracts result links and snippets from DDG Lite markup
  - Shared html_helpers.go with extractAttr, stripHTML, htmlUnescape

- GitHub: uses public Search API (repos, sorted by stars)
  - No auth required (10 req/min unauthenticated)
  - Shows stars, language, topics, last updated date
  - Paginated via GitHub's page parameter

- Reddit: uses public JSON search API
  - Respects safesearch (skips over_18 posts)
  - Shows subreddit, score, comment count
  - Links self-posts to the thread URL

- Bing: scrapes web search HTML (b_algo containers)
  - Extracts titles, URLs, and snippets from Bing's result markup
  - Handles Bing's tracking URL encoding

- Updated factory, config defaults, and config.example.toml
- Full test suite: unit tests for all engines, HTML parsing tests,
  region mapping tests, live request tests (skipped in short mode)

9 engines total: wikipedia, arxiv, crossref, braveapi, qwant,
duckduckgo, github, reddit, bing

internal/engines/reddit.go

@@ -0,0 +1,120 @@
+package engines
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"github.com/ashie/gosearch/internal/contracts"
+)
+
+// RedditEngine searches Reddit posts via the public JSON API.
+type RedditEngine struct {
+	client *http.Client
+}
+
+func (e *RedditEngine) Name() string { return "reddit" }
+
+func (e *RedditEngine) Search(ctx context.Context, req contracts.SearchRequest) (contracts.SearchResponse, error) {
+	if strings.TrimSpace(req.Query) == "" {
+		return contracts.SearchResponse{Query: req.Query}, nil
+	}
+	if e == nil || e.client == nil {
+		return contracts.SearchResponse{}, errors.New("reddit engine not initialized")
+	}
+
+	endpoint := fmt.Sprintf(
+		"https://www.reddit.com/search.json?q=%s&limit=25&sort=relevance&t=all",
+		url.QueryEscape(req.Query),
+	)
+
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	httpReq.Header.Set("User-Agent", "gosearch/0.1 (compatible; +https://git.ashisgreat.xyz/penal-colony/gosearch)")
+
+	resp, err := e.client.Do(httpReq)
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
+		return contracts.SearchResponse{}, fmt.Errorf("reddit api error: status=%d body=%q", resp.StatusCode, string(body))
+	}
+
+	var data struct {
+		Data struct {
+			Children []struct {
+				Data struct {
+					Title      string `json:"title"`
+					URL        string `json:"url"`
+					Permalink  string `json:"permalink"`
+					Score      int    `json:"score"`
+					NumComments int   `json:"num_comments"`
+					Subreddit  string `json:"subreddit"`
+					CreatedUTC float64 `json:"created_utc"`
+					IsSelf     bool   `json:"is_self"`
+					Over18     bool   `json:"over_18"`
+				} `json:"data"`
+			} `json:"children"`
+		} `json:"data"`
+	}
+
+	if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
+		return contracts.SearchResponse{}, err
+	}
+
+	results := make([]contracts.MainResult, 0, len(data.Data.Children))
+	for _, child := range data.Data.Children {
+		post := child.Data
+
+		// Skip NSFW results unless explicitly allowed.
+		if post.Over18 && req.Safesearch > 0 {
+			continue
+		}
+
+		// For self-posts, link to the Reddit thread.
+		linkURL := post.URL
+		if post.IsSelf || strings.HasPrefix(linkURL, "/r/") {
+			linkURL = "https://www.reddit.com" + post.Permalink
+		}
+
+		content := fmt.Sprintf("r/%s · ⬆ %d · 💬 %d", post.Subreddit, post.Score, post.NumComments)
+		if req.Safesearch == 0 {
+			// No additional content for safe mode
+		}
+
+		title := post.Title
+		urlPtr := linkURL
+
+		results = append(results, contracts.MainResult{
+			Template: "default.html",
+			Title:    title,
+			Content:  content,
+			URL:      &urlPtr,
+			Engine:   "reddit",
+			Score:    float64(post.Score),
+			Category: "general",
+			Engines:  []string{"reddit"},
+		})
+	}
+
+	return contracts.SearchResponse{
+		Query:               req.Query,
+		NumberOfResults:    len(results),
+		Results:             results,
+		Answers:             []map[string]any{},
+		Corrections:         []string{},
+		Infoboxes:           []map[string]any{},
+		Suggestions:         []string{},
+		UnresponsiveEngines: [][2]string{},
+	}, nil
+}