Members joining via workspace invite share the owner's account_id.
ProfileController::destroy was unconditionally calling $account->delete()
in every profile-deletion path, so any member could wipe the whole
organization (cascade: workspaces, posts, social accounts, signatures,
labels) just by clicking Delete on their own profile.
Gate the account/subscription teardown behind isAccountOwner(). For
members the path now only detaches them from workspaces and deletes
the user row — owner's data is untouched.
Tested in both SELF_HOSTED=true and false.
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