Document that Draupnir needs a Moderator power level in a hand-created management room

Draupnir stores each protection's settings as custom state events in the
management room, which requires a power level of 50 by default. A bot left
at the default power level of 0 cannot save any protection settings.

The failure is silent and has an expensive symptom: the
PolicyChangeNotification protection cannot remember its notifications room,
so it creates a brand new one on every restart of the bot. With the
playbook restarting the bot on every installation run, this litters the
server with abandoned rooms (90 of them observed on one deployment over
6 months).

Zero Touch Deployment is unaffected, since the bot creates and owns the
management room itself.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/configuring-playbook-bot-draupnir.md

@@ -39,6 +39,8 @@ Using your own account, create a new invite only room that you will use to manag
 > [!WARNING]
 > Anyone in this room can control the bot so it is important that you only invite trusted users to this room.
 
+The bot also needs at least a Moderator power level (50) in this room. This power level is granted in a [later step](#create-and-invite-the-bot-to-the-management-room-only-when-using-native-login-without-zero-touch-deployment), after the bot gets invited to the room.
+
 It is possible to make the management room encrypted (E2EE). If doing so, then you need to enable the native E2EE support (see [below](#native-e2ee-support)).
 
 E2EE support for the management room is mutually exclusive with Zero Touch Deployment of Draupnir.
@@ -135,6 +137,13 @@ ansible-playbook -i inventory/hosts setup.yml --tags=setup-all,ensure-matrix-use
 
 Then, invite the bot (`@bot.draupnir:example.com`) to its management room which you have created earlier.
 
+After the bot joins, give it at least a Moderator power level (50) in the management room.
+
+> [!WARNING]
+> Draupnir stores each protection's settings as custom state events in the management room, and sending those requires a power level of 50 by default. A bot without this power level cannot save any protection settings. The failure is easy to miss and has nasty consequences: the `PolicyChangeNotification` protection, unable to remember its notifications room, will create a brand new one on every restart of the bot (and the playbook restarts it on every installation run), littering your server with abandoned rooms.
+
+This is not a concern for Zero Touch Deployment, where the bot creates the management room itself and has full control over it.
+
 ### Creating a user account for the bot (when using Zero Touch Deployment)
 
 Since Zero Touch Deployment is not validated with native login, you will need to create the user account manually.