fix: address review feedback and improve Stellar tools validation

[Feyzanur25]

Added error handling for missing parameters and improved documen## Summary

This PR improves transaction signing compatibility, TypeScript safety, and the overall reliability of multiple Stellar tools within AgentKit.

Changes

Transaction Handling

• Improved transaction/XDR handling to ensure compatibility with newer Stellar SDK versions
• Replaced outdated patterns with a unified and safer transaction building approach
• Added validation for required parameters such as txXDR and networkPassphrase

Environment Validation

• Added runtime validation for STELLAR_PRIVATE_KEY and STELLAR_PUBLIC_KEY
• Removed unsafe non-null assertions (!) on environment variables
• Improved error messages for missing configuration

Bridge Tool Improvements

• Cleaned up duplicate and unused imports from the Stellar SDK
• Simplified keypair usage to avoid redundant creation
• Improved Soroban restore transaction handling
• Improved overall readability and maintainability

Liquidity Contract Tool Fixes

• Fixed TypeScript errors caused by checking truthiness on void return values
• Improved input validation for deposit, swap, withdraw, and reserve actions
• Refactored schema typing using z.infer<typeof schema>
• Improved response consistency and control flow

Staking Contract Tool Fixes

• Fixed incorrect handling of void return values in contract calls
• Improved validation for initialize, stake, unstake, and claim flows
• Simplified execution flow and success responses
• Removed unsafe any usage in error handling

TypeScript & Code Quality

• Replaced any with safer unknown error handling patterns
• Improved type safety and schema consistency
• Fixed invalid TypeScript typing issues
• Cleaned up code structure for better maintainability

Technical Impact

• Ensures compatibility with modern Stellar SDK versions
• Prevents runtime crashes caused by missing environment variables
• Improves TypeScript correctness and developer experience
• Strengthens reliability of bridge, staking, and liquidity tools
• Makes the codebase more production-ready and maintainable

Notes

This PR focuses on improving both runtime safety and developer experience while aligning the codebase with current best practices for Stellar and TypeScript-based tooling.

This PR addresses review feedback from previous submission and includes additional fixes across bridge, staking, and liquidity tools.tation.

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Summary by cubic

Hardened Stellar transaction signing by validating inputs and environment variables and switching to @stellar/stellar-sdk for better compatibility and clearer errors.

• Bug Fixes
  • Validate STELLAR_PRIVATE_KEY, txXDR, and networkPassphrase; throw explicit errors when missing.
  • Switch import to @stellar/stellar-sdk and refactor signTransaction to a safer, unified pattern.
  • Add concise docs and minor cleanup to improve readability.

^{Written for commit b42ce08. Summary will update on new commits.}

[cubic-dev-ai]

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