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/logstore/provider_test.go

@@ -0,0 +1,109 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package logstore
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	analyticsmodel "github.com/Rain-kl/Wavelet/internal/model/analytics"
+)
+
+func TestMigratingReadsConfig(t *testing.T) {
+	ResetForTest()
+	SetConfigReader(func(_ context.Context, key string) (string, error) {
+		if key == logMigrationKey {
+			return "migrating", nil
+		}
+		return "", nil
+	})
+	if !Migrating(context.Background()) {
+		t.Fatal("Migrating() = false, want true when key=migrating")
+	}
+	SetConfigReader(func(_ context.Context, key string) (string, error) {
+		return "", nil
+	})
+	if Migrating(context.Background()) {
+		t.Fatal("Migrating() = true, want false when key empty")
+	}
+}
+
+func TestResolveDatabaseDefaults(t *testing.T) {
+	ResetForTest()
+	// 配置缺失（reader 返回空值）时按主库规则 seed（config.Config 默认值由既有测试基建决定）。
+	SetConfigReader(func(_ context.Context, key string) (string, error) {
+		return "", nil
+	})
+	got, err := resolveDatabase(context.Background())
+	if err != nil {
+		t.Fatalf("resolveDatabase: %v", err)
+	}
+	if got != "postgres" && got != "sqlite" && got != "clickhouse" {
+		t.Fatalf("unexpected default log database: %s", got)
+	}
+}
+
+func TestResolveDatabaseSurfacesReadError(t *testing.T) {
+	ResetForTest()
+	wantErr := errors.New("boom")
+	SetConfigReader(func(_ context.Context, key string) (string, error) {
+		return "", wantErr
+	})
+	if _, err := resolveDatabase(context.Background()); !errors.Is(err, wantErr) {
+		t.Fatalf("resolveDatabase error = %v, want %v", err, wantErr)
+	}
+}
+
+func TestActiveBuildsStore(t *testing.T) {
+	ResetForTest()
+	SetConfigReader(func(_ context.Context, key string) (string, error) {
+		if key == logDatabaseKey {
+			return "sqlite", nil
+		}
+		return "", nil
+	})
+	store, err := Active(context.Background())
+	if err != nil {
+		t.Fatalf("Active: %v", err)
+	}
+	if store == nil {
+		t.Fatal("Active() returned nil store")
+	}
+	if store.AccessLogs == nil || store.Observability == nil || store.UserAccessLogs == nil || store.Status == nil {
+		t.Fatalf("Active() store fields not fully wired: %+v", store)
+	}
+	// 再次调用应命中缓存。
+	again, err := Active(context.Background())
+	if err != nil {
+		t.Fatalf("Active (cached): %v", err)
+	}
+	if again != store {
+		t.Fatal("Active() did not return cached store")
+	}
+}
+
+// TestClickHouseUserAccessLogBatchInsertFreeze 覆盖 CH 用户访问日志 flush 的冻结检查：
+// 冻结期非空批次返回 ErrMigrating（在触碰 CH 连接之前），空批次直接成功。
+func TestClickHouseUserAccessLogBatchInsertFreeze(t *testing.T) {
+	ResetForTest()
+	SetConfigReader(func(_ context.Context, key string) (string, error) {
+		if key == logMigrationKey {
+			return "migrating", nil
+		}
+		return "", nil
+	})
+	defer ResetForTest()
+	s := newClickHouseUserAccessLogStore()
+	ctx := context.Background()
+	now := time.Now()
+
+	if err := s.BatchInsert(ctx, []analyticsmodel.UserAccessLog{{UserID: 1, CreatedAt: now}}); !errors.Is(err, ErrMigrating) {
+		t.Fatalf("BatchInsert during migration: want ErrMigrating, got %v", err)
+	}
+	if err := s.BatchInsert(ctx, nil); err != nil {
+		t.Fatalf("BatchInsert empty batch: %v", err)
+	}
+}