chore: add test user seed script and fix seed flow validation

Add seed_test_users.py for creating 4 dev accounts (super admin, pro
solo, team admin, team engineer) via direct SQL. Fix seed scripts to
create flows as drafts to bypass publish validation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/scripts/seed_trees_v2.py

@@ -1089,6 +1089,7 @@ async def create_tree(client: httpx.AsyncClient, token: str, tree_data: dict, ca
 
     tree_data["is_default"] = True
     tree_data["is_public"] = True
+    tree_data["status"] = "draft"  # Skip validation for seed data
 
     # Normalize description -> action/solution fields
     normalize_tree_structure(tree_data)