docs: add path to €15k MRR analysis (freedom number)

Commit notes

Reverse-engineered what's needed to hit €15k MRR: - Model A: 22,038 users needed (at 8% conversion) - Model B: 17,238 users needed (44% fewer than current) - Model C: 31,050 users needed

Three strategies analyzed: 1. Maximize ARPU: 400 studios at €38/mo = €15k (only 5k users) 2. Optimize conversion: 15% conversion = only 9k users needed 3. Hybrid: 10k users, 12% conversion, €12.50 ARPU

Recommended fastest path: - Phase 1: Ship two-tier now (5GB free, €9 Pro) - Phase 2: Add Team tier + annual plans - Phase 3: Add storage/seat add-ons

Key insight: Ship Model C fast, evolve to Model A in 60 days. Time saved shipping > users lost to suboptimal pricing.

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