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/Dockerfile

@@ -0,0 +1,9 @@
+FROM rust:1.87-slim
+
+RUN apt-get update && apt-get install -y build-essential pkg-config && rm -rf /var/lib/apt/lists/*
+RUN cargo install cargo-fuzz
+
+COPY . /src
+WORKDIR /src
+
+RUN cd fuzz && cargo fuzz build 2>/dev/null || true