fix(frontend): show the server's reason for each excluded RI on the exchange page #1407

renderExcludedRIsNotice (frontend/src/riexchange.ts ~593) always shows "AWS returned no term length" for every excluded RI and ignores the reason field the API already returns (frontend/src/api/riexchange.ts:64-67). #1187 added exclusions for a non-positive duration, and #1191 adds exclusions for missing pricing (errRINoPricing, internal/api/handler_ri_exchange.go ~1646-1650), so the notice shows the wrong cause for those RIs.

Fix: render the server's reason per excluded RI, keep the term-length text only as a fallback for responses that lack it, and add a jest test with one RI of each exclusion reason. #1191 should merge after this.