fix(components): handle undefined value in GitHubStarHistory formatter

Update Tooltip formatter to accept number | undefined type and handle undefined values with optional chaining and nullish coalescing.

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Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: ericyangpan

src/components/product/GitHubStarHistory.tsx

@@ -186,7 +186,10 @@ export function GitHubStarHistory({ githubUrl }: GitHubStarHistoryProps) {
                   itemStyle={{
                     color: 'var(--color-text-secondary)',
                   }}
-                  formatter={(value: number) => [`${value.toLocaleString()} stars`, 'Stars']}
+                  formatter={(value: number | undefined) => [
+                    `${value?.toLocaleString() ?? '0'} stars`,
+                    'Stars',
+                  ]}
                 />
                 <Line
                   type="monotone"