fix: remediate severity-ordered review findings across cache, scanners, and proxies

- H2: gormstore soft-delete + storage_key UNIQUE collision; re-save after eviction succeeds
- H1: cache getOrFetch cache-hit branch no longer runs CheckVulnerabilities on metadata entries
- M2: cache store() streams upstream body to temp file + SHA256 instead of double-buffering
- H3/L3: FetchResult/FetchFunc plumbing (+RequiresAuth/AuthProvider); proxy closures adapted;
        goproxy strips git+ prefix from UpstreamURL
- H4: scanner normalizes bypass package names; CheckVulnerabilities builds normalized packageKey
- M4: requireAdmin routes through extractAPIKey -> ValidateAPIKey -> admin role check
- M5: network client keeps only final RecordFailure (one count per attempt cycle)
- M3: normalizeOriginHost + buildCheckOrigin rewrite; origin_test.go added
- M1: app lifecycle cancel func; Run -> Shutdown on listen error (sole cache owner); JoinHostPort
- M6: VulnerabilityThresholds defaults all -1 so BlockOnSeverity governs
- L4: metadata.NormalizeSeverity at 4 severity-count sites (MEDIUM->MODERATE consistency)
- L1: handleDeleteBypass uses structured *errors.Error + ErrCodeNotFound
- L2: pypi extractVersionFromFilename (wheel/2nd segment, non-wheel/last digit segment);
      cacheVersion uses full unique basename; regression tests added
- L5: document per-instance ValidationCache key scoping; rename packageURL param to resource

All: go build ./... && go vet ./... && go test ./... pass; golangci-lint clean.

pkg/network/client_test.go

@@ -405,3 +405,38 @@ func TestConcurrentRequests(t *testing.T) {
 		assert.NoError(t, err)
 	}
 }
+
+// TestCircuitBreakerOpens verifies that a configured number of consecutive
+// failed requests opens the circuit breaker and that subsequent requests are
+// rejected with the circuit-open error until the breaker half-open window
+// elapses and a request succeeds again.
+func TestCircuitBreakerOpens(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer server.Close() // #nosec G104 -- Cleanup, error not critical
+
+	client := network.NewClient(network.Config{
+		Timeout:    5 * time.Second,
+		MaxRetries: 0,
+		CircuitBreaker: network.CircuitBreakerConfig{
+			Enabled:          true,
+			FailureThreshold: 3,
+			SuccessThreshold: 1,
+			Timeout:          time.Hour,
+		},
+	})
+
+	ctx := context.Background()
+
+	// Three consecutive failed requests open the breaker.
+	for i := 0; i < 3; i++ {
+		_, _, err := client.Get(ctx, server.URL, nil)
+		assert.Error(t, err)
+	}
+
+	// The next request is rejected because the breaker is open.
+	_, _, err := client.Get(ctx, server.URL, nil)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "circuit breaker is open")
+}