feat(13-02): implement MavenSource and NuGetSource with tests

- MavenSource queries Maven Central Solr API for provider keyword matches
- NuGetSource queries NuGet gallery search API with projectUrl fallback
- Both sources: httptest fixtures, ctx cancellation, metadata tests

pkg/recon/sources/maven.go

@@ -0,0 +1,118 @@
+package sources
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+	"time"
+
+	"golang.org/x/time/rate"
+
+	"github.com/salvacybersec/keyhunter/pkg/providers"
+	"github.com/salvacybersec/keyhunter/pkg/recon"
+)
+
+// MavenSource searches Maven Central for artifacts matching provider keywords.
+// Maven Central exposes a Solr-based JSON search API that requires no
+// authentication.
+type MavenSource struct {
+	BaseURL  string
+	Registry *providers.Registry
+	Limiters *recon.LimiterRegistry
+	Client   *Client
+}
+
+// Compile-time assertion that MavenSource satisfies recon.ReconSource.
+var _ recon.ReconSource = (*MavenSource)(nil)
+
+func (s *MavenSource) Name() string          { return "maven" }
+func (s *MavenSource) RateLimit() rate.Limit { return rate.Every(2 * time.Second) }
+func (s *MavenSource) Burst() int            { return 2 }
+func (s *MavenSource) RespectsRobots() bool  { return false }
+
+// Enabled always returns true: Maven Central requires no credentials.
+func (s *MavenSource) Enabled(_ recon.Config) bool { return true }
+
+// Sweep queries Maven Central's Solr search for each provider keyword and
+// emits a Finding per matching artifact.
+func (s *MavenSource) Sweep(ctx context.Context, _ string, out chan<- recon.Finding) error {
+	base := s.BaseURL
+	if base == "" {
+		base = "https://search.maven.org"
+	}
+	client := s.Client
+	if client == nil {
+		client = NewClient()
+	}
+
+	queries := BuildQueries(s.Registry, "maven")
+	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
+			}
+		}
+
+		endpoint := fmt.Sprintf("%s/solrsearch/select?q=%s&rows=20&wt=json",
+			base, url.QueryEscape(q))
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+		if err != nil {
+			return fmt.Errorf("maven: build request: %w", err)
+		}
+		req.Header.Set("Accept", "application/json")
+
+		resp, err := client.Do(ctx, req)
+		if err != nil {
+			continue // non-fatal: skip keyword on HTTP error
+		}
+
+		var parsed mavenSearchResponse
+		decErr := json.NewDecoder(resp.Body).Decode(&parsed)
+		_ = resp.Body.Close()
+		if decErr != nil {
+			continue
+		}
+
+		for _, doc := range parsed.Response.Docs {
+			if err := ctx.Err(); err != nil {
+				return err
+			}
+			src := fmt.Sprintf("https://search.maven.org/artifact/%s/%s/%s/jar",
+				doc.Group, doc.Artifact, doc.LatestVersion)
+			select {
+			case out <- recon.Finding{
+				Source:     src,
+				SourceType: "recon:maven",
+				Confidence: "low",
+				DetectedAt: time.Now(),
+			}:
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+		}
+	}
+	return nil
+}
+
+type mavenSearchResponse struct {
+	Response mavenResponseBody `json:"response"`
+}
+
+type mavenResponseBody struct {
+	Docs []mavenDoc `json:"docs"`
+}
+
+type mavenDoc struct {
+	Group         string `json:"g"`
+	Artifact      string `json:"a"`
+	LatestVersion string `json:"latestVersion"`
+}