Add toolkit leaderboard page

[Chel-Tbl]

Summary

• add a public /toolkits leaderboard page using the existing top toolkits query
• show rank, usage, toolkit group, tool count, env var count, and descriptions
• keep the patch page-only so it does not depend on other leaderboard/query PRs

Verification

• tsc --noEmit --pretty false
• targeted prettier --check for changed files
• SKIP_ENV_VALIDATION=1 next build

Note: Browser verification was blocked locally because this workspace has no .env.local and Docker is not installed in PATH, so the database-backed page cannot be served with real data here.

Closes #219