feat: Build batch health probe and account all-time usage totals

[felixszeto]

Summary

• Add an admin batch health probe for Grok Build accounts (minimal Responses hi request) with configurable probeConcurrency.
• On probe success, sync Billing and clear local waiting-reset (ClearQuotaRecovery) so accounts re-enter routing immediately.
• Classify probe failures: credential/permission → reauth; quota exhaustion → waiting-reset; rate-limit/5xx → short cooldown; invalid model → no account penalty.
• Persist per-account all-time usage totals (total_tokens / total_cost_ticks / total_requests) incremented atomically on request-audit writes, with one-time backfill from request_audits.
• Probe traffic is intentionally not audited, so it does not inflate usage totals.

Test plan

• Unit tests for relational audit usage increment + backfill guard
• Admin UI: Build accounts toolbar shows Health probe left of quota sync
• Probe success on waiting-reset account clears waiting-reset and refreshes quota display
• Probe with invalid public model name (Build/...) does not cool healthy accounts after namespace strip
• After a normal chat request, account list shows updated all-time totals
• Existing request audits remain intact after migration

[github-actions]

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