fix(manual-ledger): harden schema init race and sanitize error responses

Co-authored-by: genichin <4282227+genichin@users.noreply.github.com>

app/repositories/postgres.py

@@ -206,6 +206,7 @@ class PostgresPortfolioRepository:
     def ensure_schema(self) -> None:
         conn = self._connect()
         with conn.cursor() as cur:
+            cur.execute("SELECT pg_advisory_lock(hashtext('portfoliohub.ensure_schema.v1'))")
             cur.execute(
                 """
                 CREATE TABLE IF NOT EXISTS users (
@@ -507,6 +508,7 @@ class PostgresPortfolioRepository:
                     SELECT create_hypertable('portfolio_ledger', 'recorded_at', if_not_exists => TRUE)
                     """
                 )
+            cur.execute("SELECT pg_advisory_unlock(hashtext('portfoliohub.ensure_schema.v1'))")
 
     @staticmethod
     def _row_to_user(row: Any) -> User: