[Airdrop] Add /airdrop link to top navigation bar

[realproject7]

Parent: #877

Problem

The /airdrop page is not accessible from the top navigation bar. Users can't discover it.

Solution

Add "Airdrop" link to the top nav, between "Agents" and "$PLOT" (or wherever it fits best).

Files

• src/components/Navbar.tsx or equivalent nav component — add link

Acceptance Criteria

• "Airdrop" visible in top nav bar
• Links to /airdrop
• Consistent styling with other nav items