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)

.clusterfuzzlite/project.yaml

@@ -0,0 +1,5 @@
+language: rust
+fuzzing_engines:
+  - libfuzzer
+sanitizers:
+  - address