Service: set-password maintenance command for forgotten passwords

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -115,6 +115,8 @@ A small Rust service (axum) in `server/` keeps the user accounts (Argon2 passwor
 | `GET /api/saves/{id}` | savegame JSON |
 | `DELETE /api/saves/{id}` | delete a savegame |
 
+A forgotten password is set again on the server with `docker compose stop saves && docker compose run --rm --no-deps saves dungeoncraft-saves set-password <name> '<password>' && docker compose up -d saves` (ends the user's sessions). To start over with no accounts at all, delete `users.json` and `sessions.json` in the `savegames` volume.
+
 All requests except health and login need `Authorization: Bearer <token>`. Limits: 1 MB per savegame, 500 MB in total, 30 write requests and 20 login attempts per minute. Settings: `SAVE_DIR` (default `/data`), `LISTEN` (default `0.0.0.0:8080`).
 
 ## Adding a language