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>

cmd/flock/main.go

@@ -0,0 +1,19 @@
+// Command flock is the kubelet-invoked CNI plugin binary. It is short-lived:
+// kubelet execs it for ADD/DEL/CHECK, the binary forwards to flock-agent over
+// a unix socket, and exits.
+package main
+
+import (
+	"github.com/containernetworking/cni/pkg/skel"
+	"github.com/containernetworking/cni/pkg/version"
+
+	"code.fritzlab.net/fritzlab/flock/pkg/cni"
+)
+
+func main() {
+	skel.PluginMainFuncs(skel.CNIFuncs{
+		Add:   cni.CmdAdd,
+		Del:   cni.CmdDel,
+		Check: cni.CmdCheck,
+	}, version.All, "flock")
+}