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)

fuzz/fuzz_targets/fuzz_docker_manifest.rs

@@ -0,0 +1,8 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use nora_registry::docker_fuzz::detect_manifest_media_type;
+
+fuzz_target!(|data: &[u8]| {
+    // Fuzz Docker manifest parser — must never panic on any input
+    let _ = detect_manifest_media_type(data);
+});