review --show-board lists Opus available but calls refuse it #11

What

review --show-board reports claude-opus-5-5 as available while actual calls refuse it: one account is excluded by omp_accounts.exclude and the other has USAGE UNKNOWN. The board should reflect real eligibility and show the reason.

Why (motivation)

Misleading board wastes time diagnosing quorum failures.

User impact

Engineers running code review see a board saying a model is available, pick it, and have the call refused, which delays merging their changes until they dig out the real reason.

Cost of inaction

Quorum failures stay confusing, as with PR #8.

Acceptance criteria

• Board marks excluded or usage-unknown accounts as unavailable with a reason
• Board availability matches whether a review call is accepted

Screenshots

(none)

Deploy

Deployed: no

Links

• (none)

Skipped gates

• links: no external links needed
• links-url: no external links needed
• screenshots: no UI change in ticket