MULTI_SITE_SPEC.md described a WireGuard-mesh + live-replication design as
if unbuilt-but-planned; meanwhile theta-directory v2.2.0-v2.3.0 (rolled up
in theta-suite v2.2.0) already shipped a simpler, real join mechanism
(one-time LDIF/catalog export over a site join key, read-only spoke
enforcement, setup.sh wiring) that this doc didn't mention at all. Added a
callout pointing at docs/site-join.md as the actual current behavior, and
corrected the status table so it no longer implies unbuilt features are
implemented.
Also adds AGENT_LOCAL_DISCOVERY_SPEC.md, a standalone handoff spec for the
mDNS "prefer local discovered directory" optimization -- confirmed not
implemented anywhere in theta-agent. Needs Windows/Mac-native investigation
this environment can't do; written so it can be picked up independently.
