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/client.go

@@ -0,0 +1,12 @@
+package redis
+
+import "github.com/redis/go-redis/v9"
+
+// NewClient builds a Redis client for the given address/password/db.
+func NewClient(addr, password string, db int) *redis.Client {
+	return redis.NewClient(&redis.Options{
+		Addr:     addr,
+		Password: password,
+		DB:       db,
+	})
+}