[UX] Add tooltip to Donations explaining funds are in creator wallet

[realproject7]

Problem

Donations stat on writer dashboard shows amount but no explanation of what it means or where the funds are.

Fix

Add ⓘ tooltip next to DONATIONS label (same pattern as royalties tooltip from PR #182):

Tooltip content:
"Donations are sent directly to your wallet when donors contribute. These funds are already in your account — no claiming needed."

Files

• src/app/dashboard/writer/page.tsx (DonationCount component area)