ip-algo: rename pod field to app; image from pod spec

The `pod` field hashed pod.Name, which differs per replica because of
the ReplicaSet pod-template-hash + 5-char random suffix. With
namespace,pod,image, all replicas of the same Deployment got distinct
hextets even though they were the same workload.

Replace `pod` with `app` — a stable workload identifier derived from
the controller chain:

  - Deployment → ReplicaSet → Pod: strip the pod-template-hash suffix
    from the RS name (`traefik-789df685f` → `traefik`).
  - StatefulSet/DaemonSet/Job → Pod: use controller name as-is.
  - Bare pod: pod name.

Image now comes from pod.Spec.Containers[0].Image (the spec'd
reference). 64-hex-char values are treated as sha256 digests and
parsed as before; everything else (image:tag, short SHA) is FNV-1a-64'd
as a string. This makes `traefik:v3.5` deterministic across replicas
without needing the runtime-resolved digest.

Net effect: namespace,app,image yields identical hextets across all
replicas of the same Deployment except the trailing random N nibble.

embed.Values.Pod → App; AllocRequest.Pod kept for log context only,
new App and Image fields drive the embed call. handlers.go computes
both via deriveAppName + podImageRef helpers.

Tests: 7 new TestDeriveAppName_* cases (Deploy/STS/DS/bare/RS-without-
hash/non-controller-owner) + TestPodImageRef. Existing fuzz seeds
updated for the new keyword.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pkg/agent/ipam_test.go

@@ -148,8 +148,8 @@ func TestIPAM_AllocV6_WithEmbed(t *testing.T) {
 	}
 	i.randSrc = &fakeRand{nibbles: []byte{0xe}}
 	res, err := i.Allocate(AllocRequest{
-		ContainerID: "c1", Namespace: "mail", Pod: "stalwart-0", WantV6: true,
-		IPAlgo: []embed.Field{embed.FieldNamespace, embed.FieldPod, embed.FieldImage},
+		ContainerID: "c1", Namespace: "mail", Pod: "stalwart-0", App: "stalwart", WantV6: true,
+		IPAlgo: []embed.Field{embed.FieldNamespace, embed.FieldApp, embed.FieldImage},
 	})
 	if err != nil {
 		t.Fatalf("Allocate: %v", err)