[backlog] Codex OAuth first model discovery timeout (upstream #489)

[DeliciousBuding]

    ## Source
    - Upstream: cita-777/metapi #489
    - Matrix: `docs/analysis/original-gap-matrix.md`
    - Category: feature-protocol
    - Status: partial · Priority: P1 · Backlog: yes
    - Epic: Protocol
    - Parent: G3 #10

    ## Evidence (from matrix)
    OAuth model discovery status in `service/oauth/account.go`; first discovery timeout (~12s) constants need runtime confirm — first model discovery may time out for Codex OAuth.

    ## Acceptance criteria (draft — do not implement in G3)
    - [ ] First discovery timeout is sufficient or retry/backoff softens cold start

• Operator sees actionable status when discovery times out

• Tests cover timeout vs success discovery states

• Document recommended timeout configuration

    ## Out of scope for this issue filing
    Docs-only backlog. No product code until a later implementation wave claims this issue.