feat(web-service): allow custom access token with persisted port and localized start errors

- Persist user-supplied access token and last-used port in app_metadata, falling back to defaults when unset
- Atomically guard concurrent starts via compare_exchange with RAII rollback of the running flag
- Wrap token and port persistence in a single SeaORM transaction to prevent partial writes
- Classify bind errors (port in use, permission denied, address unavailable, invalid address) into stable i18n keys
- Localize start-failure messages across all 10 supported languages

src-tauri/src/db/service/app_metadata_service.rs

@@ -1,13 +1,13 @@
 use chrono::Utc;
 use sea_orm::sea_query::OnConflict;
-use sea_orm::DatabaseConnection;
+use sea_orm::{ConnectionTrait, DatabaseConnection};
 use sea_orm::{ActiveValue::NotSet, ColumnTrait, EntityTrait, QueryFilter, Set};
 
 use crate::db::entities::app_metadata;
 use crate::db::error::DbError;
 
-pub async fn upsert_value(
-    conn: &DatabaseConnection,
+pub async fn upsert_value<C: ConnectionTrait>(
+    conn: &C,
     key: &str,
     value: &str,
 ) -> Result<(), DbError> {