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_validation.rs

@@ -0,0 +1,13 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+use nora_registry::validation::{
+    validate_digest, validate_docker_name, validate_docker_reference, validate_storage_key,
+};
+
+fuzz_target!(|data: &str| {
+    // Fuzz all validators — they must never panic on any input
+    let _ = validate_storage_key(data);
+    let _ = validate_docker_name(data);
+    let _ = validate_digest(data);
+    let _ = validate_docker_reference(data);
+});