flock M1 scaffold: CNI plugin + agent + NodeConfig CRD

- cmd/flock + cmd/flock-agent: build cleanly; CNI ADD/DEL/CHECK return
  ErrInternal stubs until M2; agent boots, opens unix socket, logs JSON.
- pkg/agent/state.go: durable allocations.json (atomic write + fsync +
  parent fsync); pending/committed lifecycle. Tests cover round-trip,
  replace-by-cid, version mismatch, no-leak-on-tmp.
- pkg/embed/suffix.go: ip-algo IID embedding. Tests cover the /48-/96
  nibble distribution table from the design doc, determinism, prefix
  preservation, N-nibble isolation, digest-vs-fallback divergence.
- pkg/api/v1alpha1: minimal NodeConfig types (no controller-runtime yet).
- deploy/: NodeConfig CRD, empty ServiceAccount/ClusterRole, DaemonSet
  pinned to flock.fritzlab.net/agent="" label so it only runs on opted-in
  nodes.
- .gitea/workflows/main.yaml + Dockerfile: build + push to
  code.fritzlab.net/fritzlab/flock; runs go test in CI.

Design doc: dfritzlab/k8s-manager/dfritz-cni.md.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

deploy/rbac/serviceaccount.yaml

@@ -0,0 +1,26 @@
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: flock-agent
+  namespace: kube-system
+---
+# M1 RBAC: empty. The agent does not yet read any Kubernetes objects.
+# M2+ will add Pod, NetworkPolicy, and NodeConfig permissions here.
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRole
+metadata:
+  name: flock-agent
+rules: []
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRoleBinding
+metadata:
+  name: flock-agent
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: ClusterRole
+  name: flock-agent
+subjects:
+  - kind: ServiceAccount
+    name: flock-agent
+    namespace: kube-system