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)

internal/repository/analytics/access_log_stats.go

@@ -16,22 +16,13 @@ import (
 const hoursInDay = 24
 
 // DailyTrend is a single day's access count.
-type DailyTrend struct {
-	Date  string
-	Count uint64
-}
+type DailyTrend = analyticsmodel.DailyTrend
 
 // BrowserShare is a browser group's share of access logs.
-type BrowserShare struct {
-	Browser string
-	Count   uint64
-}
+type BrowserShare = analyticsmodel.BrowserShare
 
 // TopUser is an active user ranked by access count.
-type TopUser struct {
-	UserID uint64
-	Count  uint64
-}
+type TopUser = analyticsmodel.TopUser
 
 // GetDailyTrend returns per-day access counts for the last days days (inclusive of today).
 func GetDailyTrend(ctx context.Context, days int) ([]DailyTrend, error) {