replace old client with new client from commafeed-ui repository

commafeed-client/src/components/sidebar/UnreadCount.tsx

@@ -0,0 +1,18 @@
+import { Badge, createStyles } from "@mantine/core"
+
+const useStyles = createStyles(() => ({
+    badge: {
+        width: "3.2rem",
+        // for some reason, mantine Badge has "cursor: 'default'"
+        cursor: "pointer",
+    },
+}))
+
+export function UnreadCount(props: { unreadCount: number }) {
+    const { classes } = useStyles()
+
+    if (props.unreadCount <= 0) return null
+
+    const count = props.unreadCount >= 1000 ? "999+" : props.unreadCount
+    return <Badge className={classes.badge}>{count}</Badge>
+}