fix(pos): prevent null branch_id errors during sales

- process_sale now falls back to main branch when g.branch_id is missing
- Accept branch_id from request body as override
- Make update_inventory_stock trigger skip operations with NULL branch_id
- Applied updated trigger to all active tenant DBs

pos/migrations/v4.0_multi_branch.sql

@@ -230,6 +230,13 @@ ALTER TABLE cfdi_queue ALTER COLUMN sale_id DROP NOT NULL;
 CREATE OR REPLACE FUNCTION update_inventory_stock()
 RETURNS TRIGGER AS $$
 BEGIN
+    -- Skip operations that are not tied to a specific branch.
+    -- Per-branch stock tracking requires a branch_id; without it we can't
+    -- assign the stock to any location.
+    IF NEW.branch_id IS NULL THEN
+        RETURN NEW;
+    END IF;
+
     INSERT INTO inventory_stock (inventory_id, branch_id, stock)
     VALUES (NEW.inventory_id, NEW.branch_id, NEW.quantity)
     ON CONFLICT (inventory_id, branch_id) DO UPDATE