* [Servatrice] Log room channel messages and bump schema to 38
* Fixup: show room_channel audit rows and keep migration nullable
The log history query returns room_channel rows, but the log tab
dropped them. Render them in the room table with an extra Channel
column. Also drop the NOT NULL on target_type from the 37->38
migration so migrated schemas match the nullable servatrice.sql
definition (and strict-mode ALTERs cannot fail on legacy NULL rows).
Update the channel tests to the flag-based privilege model: the admin
fixture now carries IsModerator alongside IsAdmin, as the database
layer assigns.
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Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>
