/agents/<name>/config bound the working clone a config change is staged
in, so an agent could see a proposal that was never approved -- a config
that does not govern its container. Both objects already exist; this
repoints the bind at the deployed one.
Both mounts (own + child) now resolve through config_bind_source() so
they cannot drift, and agent_proposed_dir's doc-comment is corrected:
it claimed to be manager-editable and bind-mounted, and neither is true.
127846ef1b