Feature/upgradeable contract foundation

[mijinummi]

🚀 Contract Upgrade Capability Implementation (#33)

Overview

This PR introduces a secure and governance-controlled upgrade mechanism for core smart contracts, ensuring long-term maintainability without compromising user funds.

The implementation follows Soroban’s native contract upgrade pattern using update_current_contract_wasm, combined with timelock enforcement, emergency pause safeguards, and governance-controlled authorization.

This resolves the upgrade immutability risk identified in Issue #33.

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🔐 Problem Addressed

Smart contracts are immutable by default. Without an upgrade mechanism:

• Bugs cannot be patched safely
• Vulnerabilities require full redeployment and migration
• User funds may be exposed during contract replacement
• Long-term feature evolution becomes risky

This PR implements a secure upgrade architecture while preserving contract state and protecting user funds.

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🏗 Architecture Design

Soroban-Native Upgrade Pattern

Unlike EVM proxy + delegatecall, Soroban supports direct contract code replacement via:

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Issue	Title
#33	Contract Upgrade Capability	Link to this issue

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