feat(redis): add shard-aware key schema, Lua scripts, and atomic ops

Implements the kmsvc: key schema (inflight, pending/watermark keyed by
shard+partition, vis_index, dedup, fifo_lock, queue meta, shard map) plus
the atomic reap/ack Lua scripts used for safe multi-replica redelivery
and DLQ routing.

internal/redis/keys_test.go

@@ -0,0 +1,29 @@
+package redis
+
+import "testing"
+
+func TestKeyFormats(t *testing.T) {
+	cases := []struct {
+		name string
+		got  string
+		want string
+	}{
+		{"inflight", InFlightKey("orders", "rh-1"), "kmsvc:inflight:orders:rh-1"},
+		{"pending", PendingKey("orders", "0", 3), "kmsvc:pending:orders:0:3"},
+		{"watermark", WatermarkKey("orders", "0", 3), "kmsvc:watermark:orders:0:3"},
+		{"vis_index", VisIndexKey("orders"), "kmsvc:vis_index:orders"},
+		{"dedup", DedupKey("orders", "g1", "d1"), "kmsvc:dedup:orders:g1:d1"},
+		{"fifo_lock", FIFOLockKey("orders", "g1"), "kmsvc:fifo_lock:orders:g1"},
+		{"queue", QueueMetaKey("orders"), "kmsvc:queue:orders"},
+		{"shardmap", ShardMapKey("orders"), "kmsvc:shardmap:orders"},
+		{"redeliver", RedeliverKey("orders"), "kmsvc:redeliver:orders"},
+		{"queue_lock", QueueLockKey("orders"), "kmsvc:queue_lock:orders"},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			if c.got != c.want {
+				t.Errorf("got %q, want %q", c.got, c.want)
+			}
+		})
+	}
+}