feat(lending/vesu): add rewards read + claim support (BTCFi Season, DeFi Spring)

[robertkodra]

Problem

Vesu’s frontend supports campaign rewards such as BTCFi Season and DeFi Spring, but Starkzap’s current Vesu integration does not expose reward discovery or claiming.

Goal

Add optional support for Vesu rewards while keeping the existing lending architecture unchanged.

Scope

• Read wallet rewards, including campaign-level data, claimable amounts, and claim windows when available.
• Support reward claiming through the standard wallet execution flow, including both prepare and execute paths.
• Keep rewards logic isolated from the core lending, borrowing, and repayment flows.

Acceptance Criteria

• The SDK exposes a rewards read API through the Vesu integration.
• The SDK exposes a claim API with both prepare and execute support.
• Unit tests cover happy-path, unsupported, and empty-reward scenarios.
• Mainnet or sandbox e2e usage is documented with explicit safety constraints.

Notes

• Reward campaigns appear to sit outside the core V2 pool and vToken flow, so the implementation should remain modular and opt-in.