Add broker-host shared pipe staging

[wdcui]

Summary

• create one channel-provided staging resource per broker pipe
• validate endpoint direction, region offsets, lengths, and mapping size
• keep BrokerCore authoritative for bytes, capacity, rights, readiness, and closure

Stack

1. Add broker shared-memory primitives #1049 — protocol foundation
2. Add broker-host shared pipe staging #1048 — broker-host staging
3. Add broker-local shared pipe data path #1051 — broker-local data path
4. Enable shared broker pipes over Unix sockets #1050 — Unix transport enablement

[github-actions]

ℹ️ Note: This semver check was run against the wdcui/ulitebox/broker-pipe-shared-protocol branch, not main or ulitebox.

🤖 SemverChecks 🤖 No breaking API changes detected

Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.

[wdcui]

Superseded by #1052, which makes shared memory the only broker-pipe data path and consolidates the host, local, and protocol changes.