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/yandex.go

@@ -0,0 +1,177 @@
+package sources
+
+import (
+	"context"
+	"encoding/xml"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"golang.org/x/time/rate"
+
+	"github.com/salvacybersec/keyhunter/pkg/providers"
+	"github.com/salvacybersec/keyhunter/pkg/recon"
+)
+
+// YandexSource implements recon.ReconSource against the Yandex XML Search API.
+// It requires both a User and APIKey to be enabled.
+type YandexSource struct {
+	User     string
+	APIKey   string
+	BaseURL  string
+	Registry *providers.Registry
+	Limiters *recon.LimiterRegistry
+	client   *Client
+}
+
+// Compile-time assertion.
+var _ recon.ReconSource = (*YandexSource)(nil)
+
+// NewYandexSource constructs a YandexSource with the shared retry client.
+func NewYandexSource(user, apiKey string, reg *providers.Registry, lim *recon.LimiterRegistry) *YandexSource {
+	return &YandexSource{
+		User:     user,
+		APIKey:   apiKey,
+		BaseURL:  "https://yandex.com",
+		Registry: reg,
+		Limiters: lim,
+		client:   NewClient(),
+	}
+}
+
+func (s *YandexSource) Name() string          { return "yandex" }
+func (s *YandexSource) RateLimit() rate.Limit { return rate.Every(1 * time.Second) }
+func (s *YandexSource) Burst() int            { return 1 }
+func (s *YandexSource) RespectsRobots() bool  { return false }
+
+// Enabled returns true only when both User and APIKey are configured.
+func (s *YandexSource) Enabled(_ recon.Config) bool {
+	return s.User != "" && s.APIKey != ""
+}
+
+// Sweep issues one Yandex XML search request per provider keyword and emits a
+// Finding for every <url> element in the response.
+func (s *YandexSource) Sweep(ctx context.Context, _ string, out chan<- recon.Finding) error {
+	if s.User == "" || s.APIKey == "" {
+		return nil
+	}
+	base := s.BaseURL
+	if base == "" {
+		base = "https://yandex.com"
+	}
+
+	queries := BuildQueries(s.Registry, "yandex")
+	kwIndex := yandexKeywordIndex(s.Registry)
+
+	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
+			}
+		}
+
+		endpoint := fmt.Sprintf("%s/search/xml?user=%s&key=%s&query=%s&l10n=en&sortby=rlv&filter=none&groupby=%s",
+			base,
+			url.QueryEscape(s.User),
+			url.QueryEscape(s.APIKey),
+			url.QueryEscape(q),
+			url.QueryEscape(`attr="".mode=flat.groups-on-page=50`))
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+		if err != nil {
+			return fmt.Errorf("yandex: build request: %w", err)
+		}
+		req.Header.Set("User-Agent", "keyhunter-recon")
+
+		resp, err := s.client.Do(ctx, req)
+		if err != nil {
+			if errors.Is(err, ErrUnauthorized) {
+				return err
+			}
+			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+				return err
+			}
+			continue
+		}
+
+		var parsed yandexSearchResponse
+		decErr := xml.NewDecoder(resp.Body).Decode(&parsed)
+		_ = resp.Body.Close()
+		if decErr != nil {
+			continue
+		}
+
+		provName := kwIndex[strings.ToLower(extractGoogleKeyword(q))]
+		for _, grp := range parsed.Response.Results.Grouping.Groups {
+			for _, doc := range grp.Docs {
+				if doc.URL == "" {
+					continue
+				}
+				f := recon.Finding{
+					ProviderName: provName,
+					Confidence:   "low",
+					Source:       doc.URL,
+					SourceType:   "recon:yandex",
+					DetectedAt:   time.Now(),
+				}
+				select {
+				case out <- f:
+				case <-ctx.Done():
+					return ctx.Err()
+				}
+			}
+		}
+	}
+	return nil
+}
+
+// XML response structures for Yandex XML Search API.
+type yandexSearchResponse struct {
+	XMLName  xml.Name       `xml:"yandexsearch"`
+	Response yandexResponse `xml:"response"`
+}
+
+type yandexResponse struct {
+	Results yandexResults `xml:"results"`
+}
+
+type yandexResults struct {
+	Grouping yandexGrouping `xml:"grouping"`
+}
+
+type yandexGrouping struct {
+	Groups []yandexGroup `xml:"group"`
+}
+
+type yandexGroup struct {
+	Docs []yandexDoc `xml:"doc"`
+}
+
+type yandexDoc struct {
+	URL string `xml:"url"`
+}
+
+// yandexKeywordIndex maps lowercased keywords to provider names.
+func yandexKeywordIndex(reg *providers.Registry) map[string]string {
+	m := make(map[string]string)
+	if reg == nil {
+		return m
+	}
+	for _, p := range reg.List() {
+		for _, k := range p.Keywords {
+			kl := strings.ToLower(strings.TrimSpace(k))
+			if kl == "" {
+				continue
+			}
+			if _, exists := m[kl]; !exists {
+				m[kl] = p.Name
+			}
+		}
+	}
+	return m
+}