Document alpha.6 release deployment

[suir1]

Summary

• record the official alpha.6 version, commit, binary digest, and alpha.5 rollback path
• document release workflow, browser TURN, native relay, route, doctor, and post-deploy service checks
• retain older rollback and diagnostic binaries

Verification

• downloaded release assets passed scripts/verify_release.sh
• production serve --check-config passed before replacement
• strict-TLS forced-TURN browser text/file matrix passed
• native 1 MiB service relay transfer matched SHA-256
• route and doctor returned ok
• services active; rooms and allocations empty; warning journal empty