[baylesj]

Addresses #343 (part of #341).

Summary

• §3 Metadata Discovery (Inline Issue 3): Rewrites agent-status-request / agent-status-response keep-alive and reconnection semantics in application.bs to be independent of QUIC, and moves the QUIC-specific idle_timeout (25s), PING frame, and error code 5139 guidance to network.bs.
• §4 Message delivery using CBOR (Inline Issue 4): Defines message framing and delivery in terms of [=ordered message sequences=] and [=independent messages=] rather than unidirectional QUIC streams and CONNECTION_CLOSE frames.
• §8.3–8.6 Audio, Video, Data, and Feedback (Inline Issues 8–11): Replaces QUIC stream references with [=independent messages=] and [=ordered message sequences=] (and fixes a copy-paste typo in §8.6 Feedback that referred to video frames).
• §9 Requests, Responses, and Watches (Inline Issue 12): Replaces QUIC connection references with generic transport connections and persistent authenticated peer identifiers.
• §10 Protocol Extensions & Appendix A: Replaces remaining references to QUIC streams with transport-agnostic terminology.