docs: reframe model around seller jobs-to-be-done

Commit notes

Major pivot from storage-focused to seller-focused pricing:

Jobs to be done for beat/sample pack sellers: - Create packs worth buying - List for sale easily - Get discovered (marketplace) - Keep 100% of revenue (0% fees) - Track performance - Get paid

New tier structure: - Free: 2 packs, 15% platform fee, 5GB - Seller (€9/mo): Unlimited packs, 0% fees, 100GB - Label (€29/mo): Team features, 500GB, priority placement

Revenue comparison: - Storage model: €6,805 MRR @ 10k users - Seller model: €26,250 MRR @ 10k users (3x higher!)

Path to €15k MRR: - Storage model: 22,000 users needed - Seller model: 6,000 users needed (70% fewer!)

Key insight: Breakeven for Seller tier is €60/mo in sales. Upgrade prompt: "If you sell €60/mo, it pays for itself."

Co-authored-by: armin.naimi <[email redacted]>