fix: use dark text on blue accent step-number badges across all flow types

#60a5fa (electric blue) is a light colour — near-white and muted-foreground
text on it produced ~1.9–2.1:1 contrast, well below WCAG AA.

- TreeNavigationPage: option number badges + timer badge → text-[#0e1016]
- StepChecklist: active step was blue badge on blue row (invisible); now
  inverts to navy circle with blue number when current, dark-on-blue otherwise
- StepDetail: step number circle → text-[#0e1016] (was near-white on light blue)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/procedural/StepChecklist.tsx

@@ -52,7 +52,10 @@ export function StepChecklist({ steps, currentStepIndex, completedStepIds, onSte
               ) : (
                 <Circle className="h-4 w-4 shrink-0 text-muted-foreground" />
               )}
-              <span className="flex h-5 w-5 shrink-0 items-center justify-center rounded-full bg-accent text-[10px] font-medium">
+              <span className={cn(
+                'flex h-5 w-5 shrink-0 items-center justify-center rounded-full text-[10px] font-bold',
+                isCurrent ? 'bg-[#0e1016] text-accent' : 'bg-accent text-[#0e1016]'
+              )}>
                 {index + 1}
               </span>
               <span className="min-w-0 flex-1 flex items-center gap-1.5 overflow-hidden">

frontend/src/components/procedural/StepDetail.tsx

@@ -91,7 +91,7 @@ export function StepDetail({
     <div className="space-y-4">
       {/* Step header */}
       <div className="flex items-start gap-3">
-        <span className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-accent text-sm font-semibold text-foreground">
+        <span className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-accent text-sm font-bold text-[#0e1016]">
           {stepNumber}
         </span>
         <div className="min-w-0 flex-1">