Build stake-weighted voting delegation system

[Smartdevs17]

Description

Implement a delegation system where token holders can delegate voting power to representatives, with support for multiple delegation strategies.

Acceptance Criteria

• Delegation with power calculation from stake
• Multiple delegation strategies (full, percentage, issue-specific)
• Delegation history with revoke capability
• Delegation expiration with auto-revoke
• Vote weight snapshot for governance proposals
• Delegation analytics dashboard

Technical Scope

• stellar-lend/contracts/hello-world/src/governance.rs
• api/src/services/staking.service.ts
• Edge: delegation chain depth, vote selling prevention, delegation during active votes