♻️ (seaorm): Adapta al arranque async

- Elimina `run_now` y convierte `initialize()` en `async fn`.
- `DBCONN` pasa de `LazyLock` a `OnceLock`; `MigratorBase` adopta
  `#[pagetop::async_trait]` con métodos async nativos.

extensions/pagetop-seaorm/src/migration/connection.rs

@@ -10,7 +10,7 @@ pub enum SchemaManagerConnection<'c> {
     Transaction(&'c DatabaseTransaction),
 }
 
-#[async_trait::async_trait]
+#[pagetop::async_trait]
 impl ConnectionTrait for SchemaManagerConnection<'_> {
     fn get_database_backend(&self) -> DbBackend {
         match self {
@@ -55,7 +55,7 @@ impl ConnectionTrait for SchemaManagerConnection<'_> {
     }
 }
 
-#[async_trait::async_trait]
+#[pagetop::async_trait]
 impl TransactionTrait for SchemaManagerConnection<'_> {
     async fn begin(&self) -> Result<DatabaseTransaction, DbErr> {
         match self {

extensions/pagetop-seaorm/src/migration/migrator.rs

@@ -57,7 +57,7 @@ impl Migration {
 }
 
 /// Performing migrations on a database
-#[async_trait::async_trait]
+#[pagetop::async_trait]
 pub trait MigratorTrait: Send {
     /// Vector of migrations in time sequence
     fn migrations() -> Vec<Box<dyn MigrationTrait>>;

extensions/pagetop-seaorm/src/migration/schema.rs

@@ -15,7 +15,7 @@
 //!
 //! pub struct Migration;
 //!
-//! #[async_trait::async_trait]
+//! #[pagetop::async_trait]
 //! impl MigrationTrait for Migration {
 //!     async fn up(&self, manager: &SchemaManager) -> Result<(), DbErr> {
 //!         let table = table_auto(Users::Table)