refactor(migration): delete pkg/migrator, move SQL to per-plugin embed

BREAKING: pkg/migrator/ deleted entirely. Migration SQL files are now
owned by each plugin in its own migrations/ directory.

Architecture:
- Delete pkg/migrator/ (26 global SQL files + ClickHouse migration)
- Move global SQL to per-plugin migrations/ with go:embed + Register()
- Rewrite cmd/app.go gooseEngine: uses Inject[DBService] for DB, iterates
  all plugin-registered MigrationEntry, runs goose.Up per entry
- core.MigrationEngine.Migrate signature changed: *Context instead of
  context.Context, so engine can resolve services via IoC

Per-plugin migration ownership:
  auth/             → w_access_tokens, w_auth_sources, w_external_accounts
  user/             → w_users (seed system user)
  admin/            → w_system_configs, w_templates (seeds)
  upload/           → w_uploads, w_upload_stats
  message_gateway/  → w_push_*, w_message_*
  risk_control/     → w_user_access_logs (PG + ClickHouse)
  driver_asynq_cron/  → w_schedules
  driver_asynq_worker/ → w_task_executions

Dependencies:
- cmd/banner.go: removed migration report display (migrations are automatic)
- cmd/reset_passwd.go: removed PreRun migrator.Migrate() call
- go.mod: clickhouse-go kept (used by plugins/infra/database/clickhouse.go)

cmd/reset_passwd.go

@@ -13,7 +13,6 @@ import (
 	"os"
 	"strings"
 
-	"github.com/Rain-kl/Wavelet/pkg/migrator"
 	userdomain "github.com/Rain-kl/Wavelet/plugins/domain/user"
 	"github.com/Rain-kl/Wavelet/plugins/infra/database"
 
@@ -46,12 +45,12 @@ func generateRandomPassword(length int) (string, error) {
 var resetPasswdCmd = &cobra.Command{
 	Use:   "reset-passwd",
 	Short: "重置指定账号密码",
-	PreRun: func(_ *cobra.Command, _ []string) {
-		migrator.Migrate()
-	},
 	Run: func(_ *cobra.Command, _ []string) {
 		ctx := context.Background()
 
+		// Ensure database is initialized
+		database.DB(ctx)
+
 		var username string
 		if usernameFlag != "" {
 			username = usernameFlag