[Airdrop] Update milestone tiers: add Diamond, adjust percentages, use emojis

[realproject7]

Parent: #877

Problem

Current milestones use 3 tiers with text colors that aren't visible on the cream background. Need 4 tiers with updated targets and emojis.

Updated Milestones

Milestone	Emoji	FDV Target	Pool Distributed
🥉 Bronze	🥉	$1M	10% (5,000 PLOT)
🥈 Silver	🥈	$10M	30% (15,000 PLOT)
🥇 Gold	🥇	$50M	50% (25,000 PLOT)
💎 Diamond	💎	$100M	100% (50,000 PLOT)

Changes

1. Config (lib/airdrop/config.ts): Add DIAMOND tier, change GOLD from $70M/100% to $50M/50%
2. All UI components: Replace text color indicators with emoji prefixes
3. All API responses: Include 4 tiers instead of 3
4. Finalize script (scripts/airdrop-finalize.ts): Update milestone determination logic

Files

• lib/airdrop/config.ts — update MILESTONES
• src/components/airdrop/MilestoneTrack.tsx — 4 tiers + emojis
• src/components/airdrop/CampaignHero.tsx — emojis
• src/components/airdrop/UserPoints.tsx — estimated airdrop at 4 tiers
• src/app/api/airdrop/status/route.ts — return 4 milestones
• scripts/airdrop-finalize.ts — 4-tier determination

Acceptance Criteria

• 4 milestone tiers: 🥉 🥈 🥇 💎
• FDV targets: $1M / $10M / $50M / $100M
• Pool %: 10% / 30% / 50% / 100%
• Emojis used everywhere (no text color indicators)
• Config, APIs, UI, and finalize script all updated