feat(project-calendar): add shared Month/Week badge component

src/components/project-period-badge.tsx

@@ -0,0 +1,18 @@
+// src/components/project-period-badge.tsx
+import { Badge } from "@/components/ui/badge";
+import type { ProjectPeriodLabel } from "@/lib/project-calendar";
+
+/**
+ * "M{month} · W{week}" tag for a row, or an em-dash when the row's site
+ * has no job_start_date set yet (see project-calendar.ts).
+ */
+export function ProjectPeriodBadge({ period }: { period: ProjectPeriodLabel | null }) {
+  if (!period) {
+    return <span className="text-xs text-muted-foreground">—</span>;
+  }
+  return (
+    <Badge variant="outline" className="font-mono text-[10px] whitespace-nowrap">
+      M{period.projectMonth} · W{period.projectWeek}
+    </Badge>
+  );
+}