fix: card-level buttons use ghost/outline instead of solid primary

Repeated per-card action buttons (Start Session, Resume, Save, Insert,
Start batch) now use cyan outline style to reduce visual noise.
Page-level and modal primary actions remain solid cyan.

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

frontend/src/components/dashboard/OpenSessions.tsx

@@ -52,7 +52,7 @@ export function OpenSessions({ sessions }: OpenSessionsProps) {
               <Link
                 to={getTreeNavigatePath(session.treeId, session.treeType)}
                 state={{ sessionId: session.id }}
-                className="shrink-0 rounded-lg bg-primary px-3 py-1 text-[0.6875rem] font-medium text-white hover:brightness-110 transition-opacity"
+                className="shrink-0 rounded-lg border border-primary/40 px-3 py-1 text-[0.6875rem] font-medium text-primary hover:bg-primary/10 hover:border-primary/60 transition-colors"
               >
                 Resume
               </Link>