Add K8s deployment for OCI (aarch64) and make deploy/deploy-oci targets

- K8s manifests: namespace, PVC (local-path 2Gi), deployment, service, ingress
- Ingress: repo-vis.oci.euphon.net with Let's Encrypt TLS via traefik
- Cross-compile aarch64-unknown-linux-musl for OCI ARM64 host
- make deploy: local Docker (x86_64)
- make deploy-oci: SCP binary + web dist to OCI, native docker build, k3s import
- Dockerfile accepts MUSL_TARGET build arg for multi-arch support

server/.cargo/config.toml

@@ -0,0 +1,2 @@
+[target.aarch64-unknown-linux-musl]
+linker = "aarch64-linux-gnu-gcc"