feat: Cross-pod signaling — handle rooms owned by another SFU node (tracking) #65

Cross-pod (different-node) connection handling in the Socket.IO signaling handlers

CrowdStream runs multiple SFU pods/nodes and each room is owned by exactly one node
(tracked in Redis by the room coordinator: getRedisRoom → nodeId, compared against
config.instanceId).

Today the signaling handlers do not properly handle a socket that lands on a pod
which does not own the room:

• registerBroadcaster.handler.ts — the guard exists but is stubbed with
  //TODO: Implementation for different pod connections; it just throws
  409 "Room belongs to another node".
• registerViewer.handler.ts — the ownership guard is missing entirely; these
  events operate on local room state with no node check.

This is the tracking issue for implementing real cross-pod handling (forward/proxy
signaling to the owning node, or redirect the client via sticky routing) at every
affected location. Sub-issues below.

Related: #36 (Sticky Sessions & Multi-Pod Signaling), #40 (Room→Node Placement Map in
Redis), #7 (Scalable Viewer Distribution with PipeTransport), #42 (Failover Test).

Sub-issues

registerBroadcaster.handler.ts — guard present, replace the 409 with real handling:

• feat(broadcaster): cross-pod handling in getRouterRtpCapabilities #66 getRouterRtpCapabilities (~L104)
• feat(broadcaster): cross-pod handling in createBroadcasterTransport #67 createBroadcasterTransport (~L161)
• feat(broadcaster): cross-pod handling in connectBroadcasterTransport #68 connectBroadcasterTransport (~L249)
• feat(broadcaster): cross-pod handling in produce #69 produce (~L313)

registerViewer.handler.ts — guard missing, add guard + handling:

• feat(viewer): add cross-pod guard + handling in joinRoom #70 joinRoom (~L21)
• feat(viewer): add cross-pod guard + handling in viewer:heartBeat #71 viewer:heartBeat (~L117)
• feat(viewer): add cross-pod guard + handling in createViewerTransport #72 createViewerTransport (~L137)
• feat(viewer): add cross-pod guard + handling in connectConsumerTransport #73 connectConsumerTransport (~L200)
• feat(viewer): add cross-pod guard + handling in consume #74 consume (~L229)
• feat(viewer): add cross-pod guard + handling in pauseConsumer #75 pauseConsumer (~L268)
• feat(viewer): add cross-pod guard + handling in resumeConsumer #76 resumeConsumer (~L290)