Add admin system, registration gate, mudtool database editor, and test checklist

- Add is_admin flag to player DB schema with migration for existing databases
- Add server_settings table for key-value config (registration_open, etc.)
- Add 10 in-game admin commands: promote, demote, kick, teleport, registration,
  announce, heal, info, setattitude, list — all gated behind admin flag
- Registration gate: new players rejected when registration_open=false,
  existing players can still reconnect
- Add mudtool binary with CLI mode (players/settings/attitudes CRUD) and
  interactive ratatui TUI with tabbed interface for database management
- Restructure to lib.rs + main.rs so mudtool shares DB code with server
- Add TESTING.md with comprehensive pre-commit checklist and smoke test script
- Stats and who commands show [ADMIN] badge; help shows admin section for admins

Made-with: Cursor

src/lib.rs

@@ -0,0 +1,9 @@
+pub mod admin;
+pub mod ansi;
+pub mod chargen;
+pub mod combat;
+pub mod commands;
+pub mod db;
+pub mod game;
+pub mod ssh;
+pub mod world;