fix: replace text-secondary with text-muted-foreground in branching components

In Tailwind v4, text-secondary resolves to --color-secondary (#2e3140),
a dark surface color — NOT --color-text-secondary (#848b9b). This made
all secondary text invisible on dark backgrounds.

The correct class is text-muted-foreground which maps to #848b9b.
This matches the pattern used by existing FlowPilot components.

Also reverts the unnecessary index.css variable bump from prior commit.

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

frontend/src/pages/SessionQueuePage.tsx

@@ -37,7 +37,7 @@ export default function SessionQueuePage() {
                   <span className="text-sm font-medium text-heading">{item.problem_summary || 'Untitled session'}</span>
                   {item.priority === 'elevated' && <span className="text-[10px] px-1.5 py-0.5 rounded-full bg-danger-dim text-danger">Elevated</span>}
                 </div>
-                {item.engineer_notes && <p className="text-xs text-secondary">{item.engineer_notes}</p>}
+                {item.engineer_notes && <p className="text-xs text-muted-foreground">{item.engineer_notes}</p>}
                 <div className="flex items-center gap-2 mt-1 text-xs text-muted">
                   <Clock size={10} />
                   <span>{new Date(item.created_at).toLocaleString()}</span>