release: prepare 1.0.0rc3 for Relay stability validation - #169

Summary

Prepare the third 1.0 release candidate. Refs #161, #163, #164.

• Package and generated standalone version: 1.0.0rc3 (tag v1.0.0-rc.3).
• RC3 release notes in English, Korean, Japanese and Simplified Chinese: changes since RC2 (fix(relay): diagnose route failures and safely retry setup timeouts #162 route diagnostics and bounded pre-submit setup retry; fix(relay): shorten receiver reconnect gaps and count role_busy refusals #168 receiver reconnect gaps, 10/10 keepalive and role_busy metrics), upgrade notes (no migration), install commands, evidence boundaries and the test: RC4 five-host Relay stability and real-ACK validation #164 post-publication validation plan.
• READMEs, docs indexes and release runbooks point at v1.0.0-rc.3; the RC2 candidate consistency test is replaced by an RC3 one; the translation manifest is refreshed (36 canonical documents).
• enhancement(codex): distinguish a live but not-yet-persisted Codex thread from a missing target #166 and feat(update): notify about outdated or incompatible session-peer skill installs (notice-only) #167 were deferred out of RC3 by maintainer decision.

Verification

• python -m unittest discover -s tests -t .: 513 tests, OK (11 skipped) on Python 3.14.7 and 3.13.7.
• python3 tools/generate_session_peer.py --check and git diff --check pass.

Boundaries

Merging does not publish. The draft GitHub release, publication, fleet installation and the five-host four-hour campaign follow RELEASING.md as separate steps. RC2's campaign is not a passed soak, and offline reproductions do not establish the live cause.