Implement the Djed Tefnut protocol as a simplification of Djed Shu, using the existing ETH-backed Shu contracts as the base.

Required changes:

• Remove minimum and maximum reserve ratio constraints
• Remove sellBothCoins function
• Remove linear decay mechanism of the treasury fee
• Preserve dual-oracle logic from Shu
• Ensure compatibility with existing ETH-based deployment flow

Acceptance criteria:

• Contracts compile and deploy successfully
• All removed features are fully eliminated, not just bypassed
• Core mint/redeem flows work with two oracle prices