feat(12-01): implement Shodan, Censys, ZoomEye recon sources

- ShodanSource searches /shodan/host/search with API key auth
- CensysSource POSTs to /v2/hosts/search with Basic Auth
- ZoomEyeSource searches /host/search with API-KEY header
- All use shared Client for retry/backoff, LimiterRegistry for rate limiting

pkg/recon/sources/shodan.go

@@ -0,0 +1,153 @@
+package sources
+
+import (
+	"context"
+	"encoding/json"
+	"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"
+)
+
+// ShodanSource implements recon.ReconSource against the Shodan /shodan/host/search
+// REST API. It iterates provider keyword queries and emits a Finding for every
+// match returned (exposed LLM endpoints, API keys in banners, etc.).
+//
+// A missing API key disables the source -- Sweep returns nil and Enabled reports
+// false.
+type ShodanSource struct {
+	APIKey   string
+	BaseURL  string
+	Registry *providers.Registry
+	Limiters *recon.LimiterRegistry
+	client   *Client
+}
+
+// Compile-time assertion.
+var _ recon.ReconSource = (*ShodanSource)(nil)
+
+// NewShodanSource constructs a ShodanSource with the shared retry client.
+func NewShodanSource(apiKey string, reg *providers.Registry, lim *recon.LimiterRegistry) *ShodanSource {
+	return &ShodanSource{
+		APIKey:   apiKey,
+		BaseURL:  "https://api.shodan.io",
+		Registry: reg,
+		Limiters: lim,
+		client:   NewClient(),
+	}
+}
+
+func (s *ShodanSource) Name() string          { return "shodan" }
+func (s *ShodanSource) RateLimit() rate.Limit { return rate.Every(1 * time.Second) }
+func (s *ShodanSource) Burst() int            { return 1 }
+func (s *ShodanSource) RespectsRobots() bool  { return false }
+
+// Enabled returns true only when APIKey is configured.
+func (s *ShodanSource) Enabled(_ recon.Config) bool { return s.APIKey != "" }
+
+// Sweep issues one /shodan/host/search request per provider keyword and emits
+// a Finding for every match returned.
+func (s *ShodanSource) Sweep(ctx context.Context, _ string, out chan<- recon.Finding) error {
+	if s.APIKey == "" {
+		return nil
+	}
+	base := s.BaseURL
+	if base == "" {
+		base = "https://api.shodan.io"
+	}
+
+	queries := BuildQueries(s.Registry, "shodan")
+	kwIndex := shodanKeywordIndex(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/shodan/host/search?key=%s&query=%s",
+			base, url.QueryEscape(s.APIKey), url.QueryEscape(q))
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+		if err != nil {
+			return fmt.Errorf("shodan: build request: %w", err)
+		}
+		req.Header.Set("Accept", "application/json")
+		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 shodanSearchResponse
+		decErr := json.NewDecoder(resp.Body).Decode(&parsed)
+		_ = resp.Body.Close()
+		if decErr != nil {
+			continue
+		}
+
+		provName := kwIndex[strings.ToLower(q)]
+		for _, m := range parsed.Matches {
+			f := recon.Finding{
+				ProviderName: provName,
+				Confidence:   "low",
+				Source:       fmt.Sprintf("shodan://%s:%d", m.IPStr, m.Port),
+				SourceType:   "recon:shodan",
+				DetectedAt:   time.Now(),
+			}
+			select {
+			case out <- f:
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+		}
+	}
+	return nil
+}
+
+type shodanSearchResponse struct {
+	Matches []shodanMatch `json:"matches"`
+}
+
+type shodanMatch struct {
+	IPStr string `json:"ip_str"`
+	Port  int    `json:"port"`
+	Data  string `json:"data"`
+}
+
+// shodanKeywordIndex maps lowercased keywords to provider names.
+func shodanKeywordIndex(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
+}