fix(frontend): RI exchange reshape empty state can show a stale RI count #1135

Summary

On the RI Exchange page, the reshape-recommendations empty state can show a stale convertible-RI count.

Evidence (origin/main d9b2aa7)

• loadRIExchange (frontend/src/riexchange.ts:100-146) starts loadConvertibleRIs, loadReshapeRecommendations and loadExchangeHistory in parallel.
• renderRecommendations (~:1325) builds the "All N convertible RIs meet your utilization threshold" copy from currentRIs.length.
• If the recommendations response arrives first and is empty, the copy uses the previous currentRIs (or none). Nothing re-renders it once loadConvertibleRIs updates currentRIs.

This race exists on every loadRIExchange call, including the initial page load. #285 (PR #1126) makes the post-exchange refresh go through loadRIExchange, so it is also reachable after an exchange.

Proposed fix

After the AWS Promise.all in loadRIExchange (same generation), re-render the reshape empty state when the recommendations load succeeded and returned no rows. Keep an error message from a failed recommendations load. Add a jest test that resolves recommendations before RIs and asserts the final count.

Found by CodeRabbit on PR #1126.