feat(log): decouple log storage from ClickHouse with switchable logstore

- New internal/repository/logstore abstraction: exported domain interfaces
  (AccessLogStore/ObservabilityStore/UserAccessLogStore/StatusStore),
  config-driven provider (Active/Build/Migrating/SetConfigReader), GORM
  implementation for PostgreSQL/SQLite (incl. hourly rollups computed in
  real time, migration listers, PG partition maintenance), and a ClickHouse
  wrapper preserving the native batch path; repository facade delegates to
  logstore; import-lint test enforces apps never import analyticsrepo.
- ClickHouse is now optional: the log DB is either the main DB (postgres
  when database.enabled, else sqlite) or clickhouse; boot validation +
  first-run seed; log_database / log_db_migration are protected keys.
- New user task 切换日志数据库 (of_log_db_switch): freeze log writes,
  drain batch writers, copy all 6 raw log tables by id (preserving IDs)
  with target-partition pre-creation for PG, flip log_database on success,
  clear the freeze flag on failure.
- Per-store retention (log_retention_days_*) with expiry cleanup folded
  into the daily system_cleanup task; legacy database_auto_cleanup_* and
  of_database_auto_cleanup decommissioned.
- goose migrations: 6 log tables in PG (2 monthly-partitioned) + SQLite,
  retention config seeds, schedule cleanup; GET
  /api/v1/admin/status/log-database endpoint; frontend retention settings,
  switch-task UI and status badge; changelog and docs updated.

docs(plan): log database decoupling implementation plan

docs(design): log database decoupling design (ClickHouse optional)

docs/changelog/index.md

@@ -20,6 +20,18 @@ sidebar: false
 > - Pages 无法迁移, 升级前请先手动下载并备份 Pages 静态站点的 ZIP 包，升级后重新创建。
 > - 性能调优参数重置, 升级后请重新配置
 
+## [Unreleased]
+
+### 新增
+
+- 日志存储解耦：新增日志存储抽象（`internal/repository/logstore`），ClickHouse 变为可选项，不启用时由 PostgreSQL/SQLite 承担全部日志功能；新增「切换日志数据库」任务支持 PostgreSQL/SQLite 与 ClickHouse 间数据迁移（迁移期间冻结日志写入，成功后自动切换主库并保留源数据）；日志保留时间改为按存储库在业务配置中设置（`log_retention_days_*`），过期清理并入系统垃圾清理每日任务。
+
+### 修复
+
+- 「切换日志数据库」迁移任务补齐第 6 张表（用户访问日志）的复制与清空；目标为 PostgreSQL 时按源库时间范围预建分区，历史日志可正常迁移；冻结前先排空批写入队列，避免在途日志丢失。
+- 节点监控最新指标读取仅在 ClickHouse 为当前日志库时走 ClickHouse 快速路径，日志库切换后仪表盘不再读到旧库数据。
+- `log_database` / `log_db_migration` 为受保护配置，管理端创建/修改接口均拒绝手动写入。
+
 ## [v3.4.5] - 2026-08-08
 
 ### 改进