Add factory reset admin endpoint and use it in smoke test

AGENTS.md

@@ -60,6 +60,7 @@ Do not introduce MVC controllers, Razor Pages, Blazor, or SPA frameworks.
 6. Vote phase (blind scoring)
 7. Results phase (aggregated leaderboard)
 8. Admin controls (phase switch, reset)
+9. Factory reset (clear all data including players) for fresh testing/deploy
 
 ---
 
@@ -76,4 +77,4 @@ Do not introduce MVC controllers, Razor Pages, Blazor, or SPA frameworks.
 - Implement API first, UI second
 - Keep changes small and testable
 - Prefer clarity over abstraction
-- After every iteration, do a git commit with a brief summary of the changes as a commit message.
+- After every iteration, do a git commit with a brief summary of the changes as a commit message.