feat: M8.2 Gateway Queue Adapter for SQS via api.riotpiao.com

- Unified QueueAdapter trait for concurrent dual-write operations
- GatewayQueueAdapter routes messages via api.riotpiao.com with X-Service: sqs header
- TokenProvider abstraction: StaticTokenProvider + AuthentikTokenProvider
- JWT bearer token support (from Authentik OAuth2)
- InMemoryQueueAdapter for testing
- Base64 encoding/decoding for SQS message bodies
- HTTP/REST integration (no direct gRPC complexity)
- 8 unit tests + comprehensive documentation
- Supports long-polling (ReceiveMessage), visibility timeout, DLQ

Uses standard SQS API patterns:
- SendMessage: Queue chunk for dual-write processing
- ReceiveMessage: Long-poll up to 10 messages, 20s wait
- DeleteMessage: Acknowledge on success
- ChangeMessageVisibility: Retry on failure
- SendToDLQ: After max retries

Files:
- crates/mem-cli/src/queue_adapter.rs (310 LOC)
- crates/mem-cli/src/gateway_queue_adapter.rs (530 LOC)
- tests/it_gateway_queue_adapter.rs (110 LOC)
- docs/M8.2-GATEWAY_QUEUE_ADAPTER.md (400 LOC)

crates/mem-cli/src/lib.rs

@@ -6,6 +6,9 @@ pub mod rate_limiter;
 pub mod idempotency;
 pub mod jwt_validator;
 pub mod opensearch_client;
+pub mod dual_write_indexer;
+pub mod queue_adapter;
+pub mod gateway_queue_adapter;
 pub mod query_optimizer;
 pub mod hybrid_query_worker;
 pub mod verify;