v0.3.1

## Unified 0.3.1 release

This is the first complete unified rvoip publication: all 43 publishable workspace crates are available at one version through the centralized leaf-first release graph.

Highlights:
- incorporates attributed local forks for MOQT transport/native/relay and the RTC/WebRTC stack, removing Git-only Cargo dependencies from published packages;
- preserves the public rvoip-sip API while carrying the SIP signaling cleanup and release-reporting work;
- passes locked workspace all-target checks, unit and integration tests, doctests, package validation, publication dry-runs, and registry visibility checks for all 43 crates;
- retains the immutable 108/108 beta candidate evidence from tested commit 8d44fb35. The PBX, performance, and soak gates were not rerun for the packaging-only 0.3.1 delta;
- yanks the 11 crates from the interrupted 0.3.0 train. Version 0.3.1 is the complete release to use.

Evidence and reports:
- [Beta release report](https://github.com/eisenzopf/rvoip/blob/v0.3.1/crates/sip/rvoip-sip/docs/BETA_RELEASE_REPORT.md)
- [Beta gate report](https://github.com/eisenzopf/rvoip/blob/v0.3.1/crates/sip/rvoip-sip/docs/BETA_GATE_REPORT.md)
- [Beta performance report](https://github.com/eisenzopf/rvoip/blob/v0.3.1/crates/sip/rvoip-sip/docs/BETA_PERFORMANCE_REPORT.md)

Install the unified facade with `cargo add rvoip@0.3.1`, or select any component crate at version 0.3.1.