fix: restore color/font inherit on button cards so work item titles are visible

The button wrapping from story 224 uses browser-default black text,
making titles invisible on the dark background.

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

frontend/src/components/StagePanel.tsx

@@ -187,6 +187,8 @@ export function StagePanel({
 							gap: "2px",
 							width: "100%",
 							textAlign: "left" as const,
+							color: "inherit",
+							font: "inherit",
 							cursor: onItemClick ? "pointer" : "default",
 						};
 						const cardInner = (