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/duckduckgo_parse.go

@@ -0,0 +1,112 @@
+package engines
+
+import (
+	"io"
+	"strings"
+
+	"github.com/ashie/gosearch/internal/contracts"
+)
+
+// parseDuckDuckGoHTML parses DuckDuckGo Lite's HTML response for search results.
+func parseDuckDuckGoHTML(r io.Reader) ([]contracts.MainResult, error) {
+	body, err := io.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+
+	content := string(body)
+	results := make([]contracts.MainResult, 0)
+
+	type parsedResult struct {
+		href  string
+		title string
+	}
+
+	var parsedLinks []parsedResult
+	remaining := content
+
+	for {
+		idx := strings.Index(remaining, `class="result-link"`)
+		if idx == -1 {
+			break
+		}
+
+		block := remaining[idx:]
+
+		href := extractAttr(block, "href")
+		if href == "" {
+			remaining = block[1:]
+			continue
+		}
+
+		// Skip DDG internal links.
+		if strings.HasPrefix(href, "/") || strings.Contains(href, "duckduckgo.com/l/") {
+			remaining = block[1:]
+			continue
+		}
+
+		// Extract title — text between > and </a> after the href.
+		titleStart := strings.Index(block, ">")
+		if titleStart == -1 {
+			remaining = block[1:]
+			continue
+		}
+		afterHref := block[titleStart+1:]
+		titleEnd := strings.Index(afterHref, "</a>")
+		if titleEnd == -1 {
+			remaining = block[1:]
+			continue
+		}
+		title := stripHTML(afterHref[:titleEnd])
+		title = htmlUnescape(title)
+
+		parsedLinks = append(parsedLinks, parsedResult{
+			href:  href,
+			title: title,
+		})
+
+		remaining = block[titleStart+1+titleEnd:]
+	}
+
+	// Extract snippets between results.
+	for i, link := range parsedLinks {
+		snippet := ""
+		linkIdx := strings.Index(content, link.href)
+		if linkIdx != -1 {
+			snippetRegion := content[linkIdx+len(link.href):]
+			if len(snippetRegion) > 2000 {
+				snippetRegion = snippetRegion[:2000]
+			}
+
+			snippetIdx := strings.Index(snippetRegion, "result-snippet")
+			if snippetIdx == -1 {
+				snippetIdx = strings.Index(snippetRegion, "result__snippet")
+			}
+
+			if snippetIdx != -1 {
+				snippetBlock := snippetRegion[snippetIdx:]
+				textStart := strings.Index(snippetBlock, ">")
+				if textStart != -1 {
+					textEnd := strings.Index(snippetBlock[textStart:], "</")
+					if textEnd != -1 {
+						snippet = stripHTML(snippetBlock[textStart+1 : textStart+textEnd])
+					}
+				}
+			}
+		}
+
+		urlPtr := link.href
+		results = append(results, contracts.MainResult{
+			Template: "default.html",
+			Title:    link.title,
+			Content:  snippet,
+			URL:      &urlPtr,
+			Engine:   "duckduckgo",
+			Score:    float64(len(parsedLinks) - i),
+			Category: "general",
+			Engines:  []string{"duckduckgo"},
+		})
+	}
+
+	return results, nil
+}