feat(components): implement PublishedDate component

src/components/PublishedDate.astro

@@ -0,0 +1,20 @@
+---
+import { formatISOString, formatYYMMDDString } from '../entry/date';
+
+import './PublishedDate.css';
+
+interface Props {
+  publishedAt: number;
+  className?: string;
+}
+
+const { publishedAt, className } = Astro.props;
+
+const classNames = !className ? 'PublishedDate' : `PublishedDate ${className}}`;
+const dateTime = formatISOString(publishedAt);
+const dateString = formatYYMMDDString(publishedAt);
+---
+
+<time class={classNames} datetime={dateTime}>
+  {dateString}
+</time>

src/components/PublishedDate.css

@@ -0,0 +1,4 @@
+.PublishedDate {
+  font-size: var(--font-size-note);
+  line-height: var(--line-height-note);
+}