docs(admin): clarify dav:move-calendar --force behaviour

Without --force the command fails on name conflicts and incompatible
group shares. With --force, group shares are dropped and a new name is
tried up to ten times; fails if none are free.

AI-Assisted-By: claude-sonnet-4-6
Signed-off-by: Anna Larch <anna@nextcloud.com>

Author: miaulalala

admin_manual/occ_database.rst

@@ -116,9 +116,15 @@ Move a calendar from one user to another::
 
  sudo -E -u www-data php occ dav:move-calendar personal layla fred
 
-Use ``-f`` / ``--force`` to enforce the move when there are share
-conflicts. A unique name is generated automatically if there is a
-naming conflict at the destination.
+Without ``--force``, the command fails if the destination user already
+has a calendar with the same name, or if the calendar is shared with a
+group the destination user is not a member of.
+
+Use ``-f`` / ``--force`` to proceed anyway: conflicting group shares are
+dropped, and if the calendar name is already taken at the destination a
+new name is tried automatically (``personal-1``, ``personal-2``, up to
+ten attempts). The command fails if no free name is found within those
+attempts.
 
 dav:clear-calendar-unshares
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