perf(config): add Otter RAM cache layer for system configs

Introduce pkg/cache/ram on top of existing Redis/DB config reads.
GetByKey now checks local RAM before Redis. Unified invalidation clears
RAM and Redis hash fields on admin writes, with pub/sub for multi-node
RAM eviction. Add tests and wire create/update/migrator write paths.

main.go

@@ -1,4 +1,3 @@
-// Copyright 2025 linux.do
 // Copyright 2026 Arctel.net
 // SPDX-License-Identifier: Apache-2.0