security: add cargo-fuzz targets and ClusterFuzzLite config

Fuzz targets:
- fuzz_validation: storage key, Docker name, digest, reference validators
- fuzz_docker_manifest: Docker/OCI manifest media type detection

Infrastructure:
- lib.rs exposing validation module and docker_fuzz for fuzz harnesses
- ClusterFuzzLite project config (libfuzzer + ASan)

Cargo.toml

@@ -4,6 +4,7 @@ members = [
     "nora-registry",
     "nora-storage",
     "nora-cli",
+    "fuzz",
 ]
 
 [workspace.package]