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/shardmap.go

@@ -0,0 +1,55 @@
+package redis
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"github.com/redis/go-redis/v9"
+
+	"github.com/rockliang/kafka-management-service/internal/kafka"
+)
+
+// PutShardMap writes the active shard set for a queue (design.md §4's
+// `kmsvc:shardmap:` row) and publishes an invalidation so cached readers
+// refresh. Written by the queue-operator on every reconcile that changes
+// shard membership (initial create, split, close).
+func PutShardMap(ctx context.Context, rdb *redis.Client, queue string, shards []kafka.Shard) error {
+	data, err := json.Marshal(shards)
+	if err != nil {
+		return fmt.Errorf("marshal shard map %s: %w", queue, err)
+	}
+	pipe := rdb.TxPipeline()
+	pipe.Set(ctx, ShardMapKey(queue), data, 0)
+	pipe.Publish(ctx, ShardMapChannel(queue), "invalidate")
+	if _, err := pipe.Exec(ctx); err != nil {
+		return fmt.Errorf("put shard map %s: %w", queue, err)
+	}
+	return nil
+}
+
+// GetShardMap reads the active shard set for a queue, or ok=false if the
+// queue has no shard map yet (not yet reconciled).
+func GetShardMap(ctx context.Context, rdb *redis.Client, queue string) ([]kafka.Shard, bool, error) {
+	data, err := rdb.Get(ctx, ShardMapKey(queue)).Bytes()
+	if err == redis.Nil {
+		return nil, false, nil
+	}
+	if err != nil {
+		return nil, false, fmt.Errorf("get shard map %s: %w", queue, err)
+	}
+	var shards []kafka.Shard
+	if err := json.Unmarshal(data, &shards); err != nil {
+		return nil, false, fmt.Errorf("unmarshal shard map %s: %w", queue, err)
+	}
+	return shards, true, nil
+}
+
+// DeleteShardMap removes a queue's shard map, used by the queue-operator on
+// Queue deletion.
+func DeleteShardMap(ctx context.Context, rdb *redis.Client, queue string) error {
+	if err := rdb.Del(ctx, ShardMapKey(queue)).Err(); err != nil {
+		return fmt.Errorf("delete shard map %s: %w", queue, err)
+	}
+	return nil
+}