Include archived Codex sessions in usage reports

[gt-zhangshihao03]

Summary

• scan Codex archived_sessions alongside date-partitioned active sessions
• share validation and project attribution between active and archived rollout files
• add an archived-only regression test and document both storage paths

Fixes #662

Testing

• npm test -- --run tests/providers/codex.test.ts (22 passed)
• npx tsc --noEmit
• npm test -- --run (1674 passed; one unrelated cli-status-menubar test exceeded its 5s timeout under parallel load)
• reran the timed-out test in isolation: passed in 3.03s

[ozymandiashh]

Thanks for this, @gt-zhangshihao03 — clean fix and the right approach.

It had picked up a merge conflict with main after #656 landed, so I rebased it onto current main (resolving a small README provider-table conflict) and opened #667, which supersedes this PR. Your commit authorship is preserved on the rebased branch.

On review we confirmed there's no double-counting if a session were ever present in both sessions/ and archived_sessions/ (parsing dedups on a content-based key shared across all sources), and that the new regression test genuinely covers the archived-only home (fresh temp dir with only archived_sessions/, so it exercises the readdir(sessionsDir).catch(() => []) fall-through). We'll merge from #667.