Peers were removed from core but lingered in the 9P layer.
Deleted: PeerAdd, PeerRemove, PeerList, PeerSubmit (D-Bus + manager),
peer directory listing, peer file handling, peer stat, peer
creation/removal, HasPeer, peers field on Session.
Types moved from ollie/session to ollie/agent:
AgentConfig, AgentConfigPath, AgentsDirs, BuildRuntime, Load, Event,
PersistedAgent, LoadPersistedAgent, RestoreHistory, PromptEnv,
History, Runtime, ErrInterrupted, WatchState.
ollie/session is no longer imported directly in top-level 9p/ files
or mgr/format.go and mgr/sessionfile.go (they only need agent types).
WatchAgent const inlined as string literal.
Rename the internal olliesrv/session package to olliesrv/mgr to resolve
the naming conflict with ollie/session (the core session package).
This allows importing ollie/session without an alias — the temporary
`agent "ollie/session"` scaffolding is removed. All references now
use the natural package name: session.X for core types, mgr.X for the
9P session manager.