Archive completed issue threads

[yvette-carlisle]

Summary

• archive all locally recorded terminal Codex App threads for an issue after successful completion writeback
• skip already archived attempts and leave running/continuation attempts alone
• add state-store coverage, orchestrator regression coverage, and spec wording for the archive closeout behavior

Verification

• cargo make check
• cargo make check-rust
• cargo make check-vstyle-rust
• cargo test -p decodex completed_issue_thread_archive_candidates_include_prior_terminal_attempts
• cargo test -p decodex lists_issue_attempts_and_protocol_event_presence
• cargo test -p decodex archive_thread
• cargo +nightly fmt --all -- --check
• git diff --check
• semantic drift audit