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.py

@@ -3330,6 +3330,7 @@ async def create_tree(client: httpx.AsyncClient, token: str, tree_data: dict) ->
     # Mark as default/system tree (public and visible to all)
     tree_data["is_default"] = True
     tree_data["is_public"] = True
+    tree_data["status"] = "draft"  # Skip validation for seed data
 
     # Check if tree with same name exists
     list_response = await client.get(f"{API_BASE_URL}/trees", headers=headers)