Pass skip_if_exists=True when running seed from __main__

The Cypress CI runner calls python -m transfers.seed on each run. Without
skip_if_exists, seed_all tries to insert contacts even when they already
exist from a prior run, hitting the unique constraint on (name, organization)
and crashing. The guard was already implemented in seed_all but not used
at the call site.

Author: jeremyzilar

transfers/seed.py

@@ -460,4 +460,4 @@ def seed_all(n: int = 5, skip_if_exists: bool = False):
 
 
 if __name__ == "__main__":
-    seed_all(5)
+    seed_all(5, skip_if_exists=True)