feat(11-01): add DuckDuckGoSource, YandexSource, and BraveSource

- DuckDuckGoSource scrapes HTML search (no API key, always enabled, RespectsRobots=true)
- YandexSource uses Yandex XML Search API (user+key required, XML response parsing)
- BraveSource uses Brave Search API (X-Subscription-Token header, JSON response)
- All three follow established error handling: 401 aborts, transient continues, ctx cancellation returns

pkg/recon/sources/duckduckgo.go

@@ -0,0 +1,116 @@
+package sources
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/url"
+	"regexp"
+	"time"
+
+	"golang.org/x/time/rate"
+
+	"github.com/salvacybersec/keyhunter/pkg/providers"
+	"github.com/salvacybersec/keyhunter/pkg/recon"
+)
+
+// DuckDuckGoSource implements recon.ReconSource by scraping DuckDuckGo's HTML
+// search endpoint. No API key is required -- this source is always enabled.
+//
+// It operates conservatively (2s per request) and declares RespectsRobots=true.
+type DuckDuckGoSource struct {
+	BaseURL  string
+	Registry *providers.Registry
+	Limiters *recon.LimiterRegistry
+	client   *Client
+}
+
+// Compile-time assertion.
+var _ recon.ReconSource = (*DuckDuckGoSource)(nil)
+
+// ddgResultRE matches DuckDuckGo HTML result links. The HTML search page uses
+// <a class="result__a" href="..."> anchors for organic results.
+var ddgResultRE = regexp.MustCompile(`^https?://`)
+
+// NewDuckDuckGoSource constructs a DuckDuckGoSource with the shared retry client.
+func NewDuckDuckGoSource(reg *providers.Registry, lim *recon.LimiterRegistry) *DuckDuckGoSource {
+	return &DuckDuckGoSource{
+		BaseURL:  "https://html.duckduckgo.com",
+		Registry: reg,
+		Limiters: lim,
+		client:   NewClient(),
+	}
+}
+
+func (s *DuckDuckGoSource) Name() string          { return "duckduckgo" }
+func (s *DuckDuckGoSource) RateLimit() rate.Limit { return rate.Every(2 * time.Second) }
+func (s *DuckDuckGoSource) Burst() int            { return 1 }
+func (s *DuckDuckGoSource) RespectsRobots() bool  { return true }
+
+// Enabled always returns true -- DuckDuckGo HTML scraping requires no credentials.
+func (s *DuckDuckGoSource) Enabled(_ recon.Config) bool { return true }
+
+// Sweep iterates provider keywords, scrapes DuckDuckGo HTML search, and emits
+// a Finding per result link.
+func (s *DuckDuckGoSource) Sweep(ctx context.Context, _ string, out chan<- recon.Finding) error {
+	base := s.BaseURL
+	if base == "" {
+		base = "https://html.duckduckgo.com"
+	}
+	client := s.client
+	if client == nil {
+		client = NewClient()
+	}
+
+	queries := BuildQueries(s.Registry, "duckduckgo")
+	if len(queries) == 0 {
+		return nil
+	}
+
+	for _, q := range queries {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		if s.Limiters != nil {
+			if err := s.Limiters.Wait(ctx, s.Name(), s.RateLimit(), s.Burst(), false); err != nil {
+				return err
+			}
+		}
+
+		searchURL := fmt.Sprintf("%s/html/?q=%s", base, url.QueryEscape(q))
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, searchURL, nil)
+		if err != nil {
+			return fmt.Errorf("duckduckgo: build req: %w", err)
+		}
+		req.Header.Set("User-Agent", "keyhunter-recon")
+
+		resp, err := client.Do(ctx, req)
+		if err != nil {
+			// Transient failures: continue to next query.
+			continue
+		}
+		links, parseErr := extractAnchorHrefs(resp.Body, ddgResultRE)
+		_ = resp.Body.Close()
+		if parseErr != nil {
+			continue
+		}
+
+		for _, href := range links {
+			if err := ctx.Err(); err != nil {
+				return err
+			}
+			f := recon.Finding{
+				Source:     href,
+				SourceType: "recon:duckduckgo",
+				Confidence: "low",
+				DetectedAt: time.Now(),
+			}
+			select {
+			case out <- f:
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+		}
+	}
+	return nil
+}