fix: improve text contrast in ForkCard and BranchRevivalCard

- ForkCard: fork reason → text-heading, option labels → text-heading,
  descriptions → text-primary, unselected options get bg-elevated/50
- BranchRevivalCard: evidence description → text-primary

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

frontend/src/components/session/BranchRevivalCard.tsx

@@ -16,10 +16,10 @@ export function BranchRevivalCard({ branch, evidenceSource }: BranchRevivalCardP
         <span className="text-warning font-medium">Branch Revived</span>
       </div>
       {branch.evidence_description && (
-        <p className="text-xs text-secondary mt-1">{branch.evidence_description}</p>
+        <p className="text-xs text-primary mt-1">{branch.evidence_description}</p>
       )}
       {evidenceSource && (
-        <p className="text-xs text-muted mt-0.5">Evidence from: {evidenceSource.label}</p>
+        <p className="text-xs text-secondary mt-0.5">Evidence from: {evidenceSource.label}</p>
       )}
     </div>
   )

frontend/src/components/session/ForkCard.tsx

@@ -20,7 +20,7 @@ export function ForkCard({ fork, selectedBranchId, onSelectOption }: ForkCardPro
       </div>
 
       {/* Fork reason */}
-      <p className="text-sm text-primary leading-snug">{fork.fork_reason}</p>
+      <p className="text-sm text-heading leading-snug">{fork.fork_reason}</p>
 
       {/* Options */}
       <div className="flex flex-col gap-2">
@@ -36,19 +36,22 @@ export function ForkCard({ fork, selectedBranchId, onSelectOption }: ForkCardPro
                 'hover:bg-elevated',
                 isSelected
                   ? 'border-accent bg-accent-dim'
-                  : 'border-default bg-transparent'
+                  : 'border-default bg-elevated/50'
               )}
             >
               <p
                 className={cn(
                   'text-sm font-medium',
-                  isSelected ? 'text-accent-text' : 'text-primary'
+                  isSelected ? 'text-accent-text' : 'text-heading'
                 )}
               >
                 {option.label}
               </p>
               {option.description && (
-                <p className="text-xs text-secondary mt-0.5 leading-snug">
+                <p className={cn(
+                  'text-xs mt-0.5 leading-snug',
+                  isSelected ? 'text-primary' : 'text-primary'
+                )}>
                   {option.description}
                 </p>
               )}