feat: Replace fake migration story with honest cost-benefit analysis

Rewrote the Heroku migration post to be transparent and educational:

- Changed from fake narrative to honest cost comparison
- Added Total Cost of Ownership (TCO) calculations with engineer time
- Included break-even analysis showing realistic 22-31% savings (not 90%)
- Created decision framework for when to self-host vs stay on Heroku
- Added 4 real-world scenario applications
- Honest discussion of hidden costs, risks, and tradeoffs
- Removed made-up performance metrics and migration story
- Focused on helping readers make informed decisions

Related to #927

Author: bobbyonmagic