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/config/config.go

@@ -362,6 +362,16 @@ func Default() *Config {
 		Security: SecurityConfig{
 			Enabled:         false,
 			BlockOnSeverity: "high",
+			// Default all severity caps to unlimited (-1) so the operator's
+			// BlockOnSeverity decision governs by default. A zero cap means
+			// "block any", which would make a single LOW vulnerability block
+			// every package even though the configured default is "high".
+			BlockThresholds: VulnerabilityThresholds{
+				Critical: -1,
+				High:     -1,
+				Medium:   -1,
+				Low:      -1,
+			},
 			Scanners: ScannersConfig{
 				Trivy: TrivyConfig{
 					Enabled: false,