feat(data): complete portable SQL backend parity

Align MySQL and SQLite schemas, migrations, usage, stats, export, and backfill behavior with the shared data contracts. Extend gateway startup and maintenance support across all SQL drivers.

crates/aether-data/adapters/mysql/src/pool.rs

@@ -62,6 +62,14 @@ impl MysqlPoolFactory {
             .acquire_timeout(Duration::from_millis(acquire_timeout_ms))
             .idle_timeout(Duration::from_millis(idle_timeout_ms))
             .max_lifetime(Duration::from_millis(max_lifetime_ms))
+            .after_connect(|connection, _metadata| {
+                Box::pin(async move {
+                    sqlx::query("SET time_zone = '+00:00'")
+                        .execute(connection)
+                        .await?;
+                    Ok(())
+                })
+            })
             .connect_lazy_with(self.connect_options()?))
     }
 }
@@ -90,4 +98,34 @@ mod tests {
         let factory = MysqlPoolFactory::new(config).expect("factory should build");
         let _pool = factory.connect_lazy().expect("lazy pool should build");
     }
+
+    #[tokio::test]
+    async fn factory_configures_utc_session_timezone_when_url_is_set() {
+        let Some(database_url) = std::env::var("AETHER_TEST_MYSQL_URL")
+            .ok()
+            .filter(|value| !value.trim().is_empty())
+        else {
+            eprintln!("skipping mysql timezone test because AETHER_TEST_MYSQL_URL is unset");
+            return;
+        };
+        let config = SqlDatabaseConfig {
+            driver: DatabaseDriver::Mysql,
+            url: database_url,
+            pool: SqlPoolConfig {
+                max_connections: 1,
+                ..SqlPoolConfig::default()
+            },
+        };
+
+        let pool = MysqlPoolFactory::new(config)
+            .expect("factory should build")
+            .connect_lazy()
+            .expect("lazy pool should build");
+        let timezone: String = sqlx::query_scalar("SELECT @@session.time_zone")
+            .fetch_one(&pool)
+            .await
+            .expect("mysql session timezone should load");
+
+        assert_eq!(timezone, "+00:00");
+    }
 }