Show toolkit usage in selector

[Chel-Tbl]

Summary

• let getTopToolkits accept a limit so the selector can fetch usage counts for all listed toolkits
• show each toolkit's usage count in the toolkit selector with the same Activity icon language used on the homepage
• keep the homepage top toolkits section limited through the route instead of slicing client-side

Verification

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

Closes #196