feat(protocol2): presence stream — online population + region transitions (Part B ph.2)

Overlay BridgePresence (new):
- presence.online sweep over online PlayerMobiles: total plus per-facet and
  per-region counts, emitted only when the population changes.
- region.enter real-time from EventSink.OnEnterRegion (player-filtered), the
  cheap location signal PLAN.md prefers over Movement.
- PresenceSweepSeconds (30s); wired into [bridge reload|sweepnow|status.

Sidecar:
- GET /online serves the latest presence.online snapshot from the event store
  (survives restart); population time series via /history?kind=presence.online.

Docs: INTEGRATION.md presence events + /online endpoint; PROTOCOL_2 ph.2 built.

Verified: sidecar cargo check clean; overlay compiles in the full ServUO
Scripts tree (0 errors, 0 warnings). Live run pending.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

overlay/Config/Bridge.cfg

@@ -39,6 +39,15 @@ GuildSweepSeconds=60
 # Idle (emits nothing) unless the City Loyalty system is enabled (CityLoyalty.Enabled).
 CitySweepSeconds=300
 
+# Presence poll. Online population (total, per-facet, per-region) is snapshotted on this
+# interval and emitted as presence.online only when it changes. Region transitions come
+# through separately in real time as region.enter (EventSink.OnEnterRegion).
+PresenceSweepSeconds=30
+
+# Housing registry poll. Every house is diffed on this interval to emit house.update /
+# house.remove (owner, region, location, decay). Houses change slowly; a few minutes is fine.
+HousingSweepSeconds=300
+
 # Shown to a player when they run [link. The website page where they enter the code.
 LinkUrl=https://yoursite/link