Feature/issue 63 verification and fixes

[Robinsonchiziterem]

#63 Pull Request: Structured Error Mapping & Project Stability Fixes

Overview

This PR implements structured error handling for the backend (Issue #63) and resolves several project-wide build and stability issues discovered during verification.

Key Changes

🛡️ Backend (Issue #63)

• Centralized Error Handling: Introduced ApiError class for consistent { error, message, details?, requestId } responses.
• Soroban Mapping: The global error handler now maps specific Soroban contract error codes (#1–13) to appropriate HTTP status codes (400, 403, 404, 409) and human-readable messages.
• Infrastructure Safety: Added handled cases for Soroban simulation failures (502) and missing server configurations (503).
• Refactored Routes: Simplified splits.ts by removing duplicated try-catch blocks and using validateRequest middleware for unified Zod validation.

🎨 Frontend Stability

• Fixed Build Failure: Added missing @tailwindcss/postcss, autoprefixer, and postcss dependencies required for Next.js Turbopack.
• TypeScript Bug Fix: Corrected a type mismatch in split-app.tsx where an XDR result was being passed directly to the Error constructor; it now correctly uses errorResult?.toString().
• Verified Build: Confirmed npm run build and npm run lint now pass with Exit Code 0.

📜 Contracts

• SDK Update: Bumped soroban-sdk to 21.0.0 to resolve dependency conflicts (specifically proc-macro2) with modern Rust toolchains.

Verification Results

• Backend: Verified all error mappings using a custom verify-errors.ts script (all 13 contract codes mapped correctly).
• Frontend: Successfully completed a full production build and lint.
• Backend Build: npm run build and npm run lint pass.

Related Issues

Closes #63