fix: invalidate leaderboard cache when settings change

[Saksham-Joshi856]

Related Issue

Fixes #2497

Problem

When a user disabled leaderboard participation from Settings, the leaderboard could continue showing stale data until refresh.

Root Cause

The leaderboard cache was invalidated using revalidateTag("leaderboard"), but the unstable cache entry was not associated with the "leaderboard" tag.

Because of this, cache invalidation did not reliably refresh leaderboard data.

Solution

Added the leaderboard cache tag to the unstable_cache configuration.

Now:

• leaderboard cache is tagged with "leaderboard"
• settings changes can correctly invalidate cached leaderboard data
• users opting in/out of leaderboard visibility see updated results immediately

Testing

• ✅ npm run build
• ⚠️ npm test has existing unrelated failures in Anthropic service mocking

[github-actions]

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[github-actions]

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