fix: connection pool exhaustion + cross_ref column name

- tenant_db.py: add rollback() before returning conn to pool to prevent
  'idle in transaction (aborted)' state that exhausts the pool
- tenant_db.py: increase pool maxconn from 10 to 20 for better concurrency
- inventory_vehicle_compat.py: fix column name cross_ref_number ->
  cross_reference_number to match actual schema

pos/tenant_db.py

@@ -21,7 +21,7 @@ def _get_master_pool():
     global _master_pool
     if _master_pool is None:
         _master_pool = pool.ThreadedConnectionPool(
-            minconn=2, maxconn=10, dsn=MASTER_DB_URL
+            minconn=2, maxconn=20, dsn=MASTER_DB_URL
         )
     return _master_pool
 
@@ -32,7 +32,7 @@ def _get_tenant_pool(db_name):
     if db_name not in _tenant_pools:
         dsn = TENANT_DB_URL_TEMPLATE.format(db_name=db_name)
         _tenant_pools[db_name] = pool.ThreadedConnectionPool(
-            minconn=2, maxconn=10, dsn=dsn
+            minconn=2, maxconn=20, dsn=dsn
         )
     return _tenant_pools[db_name]
 
@@ -52,6 +52,15 @@ class _PooledConnection:
 
     def close(self):
         try:
+            # Rollback any aborted transaction before returning to pool.
+            # Without this, failed transactions leave connections in
+            # 'idle in transaction (aborted)' state, eventually exhausting
+            # the pool.
+            if self._conn:
+                try:
+                    self._conn.rollback()
+                except Exception:
+                    pass
             self._pool.putconn(self._conn)
         except Exception:
             # If pool is already closed, fall back to real close