feat: Implement Stellar Yield Enhancements (Issues #35 #36 #40 #41)

[ChaoLing140]

Summary

This PR implements multiple enhancements to StellarYield as outlined in issues #35, #36, #40, and #41:

Issue #35: StellarYield Developer SDK (TypeScript)

• Created /packages/sdk with TypeScript package structure
• Implemented VaultClient for vault contract interactions (deposit, withdraw, getShares, etc.)
• Implemented ApiClient for backend API calls (APY, TVL, historical data)
• Set up tsup for ESM and CommonJS bundling
• Added comprehensive TSDoc comments for all public methods
• Included example usage in /packages/sdk/src/examples/basic.ts

Issue #36: Advanced Slippage & MEV Protection

• Added min_shares_out parameter to vault deposit functions
• Implemented on-chain slippage checks that revert if exceeded
• Added slippage tolerance UI slider (0.1% to 5%) in ZapDepositPanel
• Zap contract now passes slippage parameters through to vault

Issue #40: GraphQL API Layer

• Set up GraphQL schema with graphql-yoga at /server/src/graphql/
• Defined schemas for Vault, User, Transaction, and YieldSnapshot
• Implemented resolvers with efficient database queries (N+1 prevention)
• Integrated GraphQL endpoint in Express app

Issue #41: EIP-4626 Style Vault Standard

• Expanded VaultStandard trait in /contracts/interfaces/vault_standard.rs
• Added preview_withdraw, preview_redeem, and share_price methods
• Implemented proper rounding rules:
  • Deposits: round UP (favor vault)
  • Withdrawals: round DOWN (favor user)
• Added public view functions for all new methods

Test Plan

• SDK package compiles and exports correctly
• GraphQL resolvers properly query databases
• Vault contract implements all VaultStandard trait methods
• Slippage UI slider correctly passes parameters

Closes #35
Closes #36
Closes #40
Closes #41

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[edehvictor]

@ChaoLing140 resolve conflict