Close first threshold claim by default on compose screen

Drop the defaultOpen={i===0} on the first threshold_claim — when a
case has a lot of material already on screen (research background
+ chair positions + now precedents), auto-opening the first card
creates a wall of text on page load. All cards now start collapsed,
same as the issues list already did.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web-ui/src/app/cases/[caseNumber]/compose/page.tsx

@@ -146,12 +146,11 @@ export default function ComposePage({
                       </span>
                     </div>
                     <div className="space-y-3">
-                      {analysis.data.threshold_claims.map((tc, i) => (
+                      {analysis.data.threshold_claims.map((tc) => (
                         <SubsectionCard
                           key={tc.id}
                           caseNumber={caseNumber}
                           item={tc}
-                          defaultOpen={i === 0}
                           precedents={precedentsBySection.get(tc.id) ?? []}
                           practiceArea={practiceArea}
                         />