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/github.go

@@ -0,0 +1,120 @@
+package engines
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"github.com/ashie/gosearch/internal/contracts"
+)
+
+// GitHubEngine searches GitHub repositories and code via the public search API.
+// No authentication required (rate-limited to 10 requests/min unauthenticated).
+type GitHubEngine struct {
+	client *http.Client
+}
+
+func (e *GitHubEngine) Name() string { return "github" }
+
+func (e *GitHubEngine) 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("github engine not initialized")
+	}
+
+	endpoint := fmt.Sprintf(
+		"https://api.github.com/search/repositories?q=%s&sort=stars&per_page=10&page=%d",
+		url.QueryEscape(req.Query),
+		req.Pageno,
+	)
+
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	httpReq.Header.Set("User-Agent", "gosearch/0.1")
+	httpReq.Header.Set("Accept", "application/vnd.github.v3+json")
+
+	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("github api error: status=%d body=%q", resp.StatusCode, string(body))
+	}
+
+	var data struct {
+		TotalCount int `json:"total_count"`
+		Items      []struct {
+			FullName    string    `json:"full_name"`
+			Description string    `json:"description"`
+			HTMLURL     string    `json:"html_url"`
+			Stars       int       `json:"stargazers_count"`
+			Language    string    `json:"language"`
+			UpdatedAt   time.Time `json:"updated_at"`
+			Topics      []string  `json:"topics"`
+		} `json:"items"`
+	}
+
+	if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
+		return contracts.SearchResponse{}, err
+	}
+
+	results := make([]contracts.MainResult, 0, len(data.Items))
+	for _, item := range data.Items {
+		content := item.Description
+		if item.Language != "" {
+			if content != "" {
+				content += " • "
+			}
+			content += fmt.Sprintf("Language: %s · ⭐ %d", item.Language, item.Stars)
+		}
+
+		title := item.FullName
+		if len(item.Topics) > 0 {
+			title = item.FullName + " [" + strings.Join(item.Topics[:min(3, len(item.Topics))], ", ") + "]"
+		}
+
+		updatedAt := item.UpdatedAt.Format("2006-01-02")
+		if content != "" {
+			content += " · Updated: " + updatedAt
+		}
+
+		urlPtr := item.HTMLURL
+		results = append(results, contracts.MainResult{
+			Template: "default.html",
+			Title:    title,
+			Content:  content,
+			URL:      &urlPtr,
+			Pubdate:  strPtr(updatedAt),
+			Engine:   "github",
+			Score:    float64(item.Stars),
+			Category: "it",
+			Engines:  []string{"github"},
+		})
+	}
+
+	return contracts.SearchResponse{
+		Query:               req.Query,
+		NumberOfResults:    data.TotalCount,
+		Results:             results,
+		Answers:             []map[string]any{},
+		Corrections:         []string{},
+		Infoboxes:           []map[string]any{},
+		Suggestions:         []string{},
+		UnresponsiveEngines: [][2]string{},
+	}, nil
+}
+
+func strPtr(s string) *string { return &s }