Build comprehensive governance system with proposal lifecycle

[Smartdevs17]

Description

Create an on-chain governance system with proposal creation, voting, timelock execution, and delegation to enable protocol parameter adjustment.

Acceptance Criteria

• Proposal creation with executable calldata
• Token-weighted voting with delegation
• Voting period with configurable duration (3-14 days)
• Quorum requirement with minimum participation
• Timelock execution (min 48h delay)
• Proposal cancellation by guardian

Technical Scope

• stellar-lend/contracts/hello-world/src/governance.rs
• stellar-lend/contracts/lending/src/governance.rs
• stellar-lend/contracts/hello-world/src/governance_test.rs
• Edge: flash loan voting attack, proposal frontrunning, governance parameter change during vote