#91 feat: add inter-pod viewer transport creation

Closes: #72

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Summary by cubic

Fixes cross-pod createViewerTransport so it works when the viewer's socket and the room are on different pods. The request is now forwarded over Redis to the owning pod, which creates the transport and returns the result. Closes #72.

• When the room's Redis node differs from the local instance, the handler publishes a createViewerTransport command with a request ID and 5-second timeout.
• podConnection.ts handles the command on the owning pod, creates a consumer transport, and publishes the response back.
• The requesting pod acks the client with transport data and stores the transport ID in the Viewer document.
• Adds docs/MultiplePodSignaling/createViewerTransport.md documenting the flow.