docs: update minimum base fee to 2,000,000 wei

[niran]

Summary

• Increases minimum base fee from 1,000,000 wei to 2,000,000 wei (0.002 gwei)
• Adds changelog entry for February 2, 2026
• Updates cost reference example to ~0.1 cents for 200k gas at $2500 ETH

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1