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/clickhouse_stats.go

@@ -9,21 +9,12 @@ import (
 
 	"github.com/Rain-kl/Wavelet/internal/infra/config"
 	db "github.com/Rain-kl/Wavelet/internal/infra/persistence"
-	"github.com/Rain-kl/Wavelet/internal/infra/persistence/batchwriter"
+	analyticsmodel "github.com/Rain-kl/Wavelet/internal/model/analytics"
 )
 
 // ClickHouseOperationalStats summarizes ClickHouse merge/mutation pressure
 // and in-process batch writer queue health.
-type ClickHouseOperationalStats struct {
-	Database         string `json:"database"`
-	ActiveParts      int64  `json:"active_parts"`
-	TotalRows        int64  `json:"total_rows"`
-	PendingMutations int64  `json:"pending_mutations"`
-	AsyncInsertQueue int64  `json:"async_insert_queue"`
-	AsyncInsertBytes int64  `json:"async_insert_bytes"`
-	// BatchWriters reports in-process queue depth/drops/flush errors for CH writers.
-	BatchWriters []batchwriter.Stats `json:"batch_writers,omitempty"`
-}
+type ClickHouseOperationalStats = analyticsmodel.ClickHouseOperationalStats
 
 // GetClickHouseOperationalStats returns operational metrics for the configured database.
 func GetClickHouseOperationalStats(ctx context.Context) (*ClickHouseOperationalStats, error) {