refactor(server): remove DatabaseService.transaction — every transaction runs through UnitOfWork

server/src/nest/README.md

@@ -914,8 +914,9 @@ cycle seams are folded, nothing on the websocket path imports one, and the
 crons all inject now (`*.job.ts` providers on `scheduling/CronRegistrarService`).
 
 1. **Move the SQL** into `<domain>.service.ts` as methods over an injected
-   `DatabaseService` (`this.db.all<T>/get<T>/run/prepare/transaction`; strict
-   constructor injection, no `@Optional()`). Preserve every quirk: falsy-coercion
+   `DatabaseService` (`this.db.all<T>/get<T>/run/prepare`; multi-statement writes go
+   through `await this.uow.transactional(...)` instead — see the root `CLAUDE.md`;
+   strict constructor injection, no `@Optional()`). Preserve every quirk: falsy-coercion
    defaults (`x || fallback`, never `??`), post-insert/post-update re-selects (no
    RETURNING), `COALESCE` semantics. If a controller already wraps the legacy
    functions, do not change the service's method surface. The module needs no

server/src/nest/database/database.service.ts

@@ -38,11 +38,6 @@ export class DatabaseService {
     return this.conn.prepare(sql).run(...params);
   }
 
-  /** Run `fn` inside a synchronous better-sqlite3 transaction. */
-  transaction<T>(fn: (conn: Database.Database) => T): T {
-    return this.conn.transaction(() => fn(this.conn))();
-  }
-
   // Trip-access helpers delegate to the db/database exports (not this.conn):
   // tests vi.mock that module and stub the helpers themselves, so the stubs
   // must keep flowing through here.