feat(matrixbot): stop auto-joining invites, restrict commands to two rooms

#general is now published to the public room directory, so the bot is
reachable by strangers. Two hardening changes:

- Invites are only accepted from INVITE_ALLOWED_USERS (defaults to
  ADMIN_USERS). Anything else is declined via room_leave so hostile
  invites do not accumulate as pending. Previously any invite from
  anyone was auto-joined.
- Commands and the passive scramble/riddle answer checks only run in
  COMMAND_ROOMS (#commands and #management). The gate sits early in
  Callbacks.message, so the bot stays silent everywhere else, including
  #general. Set COMMAND_ROOMS="*" to restore the old behaviour.

Reaction handlers are deliberately left ungated so the welcome flow
keeps working; game votes elsewhere cannot match an active game.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

matrixbot/callbacks.py

@@ -3,7 +3,7 @@ from functools import wraps
 
 from nio import AsyncClient
 
-from config import BOT_PREFIX, MATRIX_USER_ID
+from config import BOT_PREFIX, COMMAND_ROOMS, MATRIX_USER_ID
 from commands import (
     COMMANDS,
     metrics,
@@ -50,6 +50,12 @@ class Callbacks:
         if event.sender == MATRIX_USER_ID:
             return
 
+        # Only act in designated command rooms. This covers both prefixed
+        # commands and the passive game-answer checks below, so the bot never
+        # speaks in public rooms such as #general. "*" allows every room.
+        if "*" not in COMMAND_ROOMS and room.room_id not in COMMAND_ROOMS:
+            return
+
         body = event.body.strip() if event.body else ""
 
         # Check active non-command games that monitor all room messages