Why

Users can see that reset credits are available, but not which credits they have, when each one expires, or which credit will be consumed.

What changed

• load reset-credit details only when the user opens Redeem usage limit reset
• show every returned available credit, sorted by expiry, with its reset scope and expiration time
• consume the exact selected credit and preserve its idempotency key across retries
• fall back to a generic Use any reset option when the backend reports more credits than its capped detail response
• keep the picker usable when either the detail request or the existing rate-limit request fails
• handle a selected credit becoming unavailable without incorrectly caching the user's total count as zero
• leave passive startup and status refreshes on the existing count-only path

TUI preview

Rendered from the final standard-width and narrow insta snapshots in this PR.

Validation

• just test -p codex-tui chatwidget::tests::usage (32 passed)
• just test -p codex-tui app::background_requests::tests::reset_credit_results (1 passed)
• just test -p codex-tui (2,955 passed; 2 pre-existing Guardian feature-flag tests failed and reproduce without this change)
• just fix -p codex-tui
• just fmt
• no pending snapshots
• Autoreview: clean

Depends on #30395.

Fixes #29618.