fix: fix DDG and Bing parsers — verified with live tests

DuckDuckGo:
- Fixed parser to handle single-quoted class attributes (class='result-link')
- Decode DDG tracking URLs (uddg= parameter) to extract real URLs
- Match snippet extraction to actual DDG Lite HTML structure (</td> terminator)

Bing:
- Switched from HTML scraping (blocked by JS detection) to RSS endpoint
  (?format=rss) which returns parseable XML
- Added JSON API response parsing as fallback
- Returns graceful unresponsive_engines entry when blocked

Live test results:
- DuckDuckGo: 9 results ✅
- GitHub: 10 results (14,768 total) ✅
- Bing: 10 results via RSS ✅
- Reddit: skipped (403 from sandbox, needs browser-like context)

internal/engines/duckduckgo_test.go

@@ -71,10 +71,10 @@ func TestDuckDuckGoRegion(t *testing.T) {
 }
 
 func TestParseDuckDuckGoHTML(t *testing.T) {
-	html := `<a class="result-link" href="https://example.com">Example Title</a>
-	<span class="result-snippet">This is a test snippet</span>
-	<a class="result-link" href="https://example2.com">Second Result</a>
-	<span class="result-snippet">Another snippet here</span>`
+	html := `<a class='result-link' href="https://example.com">Example Title</a>
+	<td class='result-snippet'>This is a test snippet</td>
+	<a class='result-link' href="https://example2.com">Second Result</a>
+	<td class='result-snippet'>Another snippet here</td>`
 
 	results, err := parseDuckDuckGoHTML(strings.NewReader(html))
 	if err != nil {