feat: add GitHub Actions lint workflow (#64)

[cyber-excel10]

Closes #64

Description

Add comprehensive linting and formatting infrastructure across all three project layers (frontend, backend, smart contracts).

This PR establishes consistent code quality standards and automated checks to catch issues early in the development process.

Changes Made

CI/CD Pipeline

• Create .github/workflows/lint.yml with parallel jobs for frontend, backend, and contracts
• Frontend job: ESLint + Prettier format checks
• Backend job: ESLint + Prettier format checks
• Contracts job: Cargo clippy + rustfmt checks

Frontend

• Fix lint script to use next lint instead of invalid command
• Add format and format:check scripts using Prettier
• Ensure ESLint and Prettier configurations are in place

Backend

• Add ESLint configuration with TypeScript support
• Add Prettier format scripts to package.json
• Configure TypeScript with proper module resolution
• All linting and formatting checks pass locally

Smart Contracts

• Upgrade soroban-sdk from 20.0.0 to 22.0.0
• Fix Cargo.toml dev-dependencies configuration
• Add #[contracterror] attribute to TokenError enum with explicit discriminants
• Ensure all Rust code passes clippy and rustfmt checks

Shared Configuration

• Add .prettierrc at repo root with consistent formatting rules:
  • semi: true
  • singleQuote: true
  • tabWidth: 2
  • trailingComma: "es5"
  • printWidth: 100

Verification

All three lint jobs verified locally:

• ✅ cargo clippy --all-targets --all-features - clean
• ✅ cargo fmt --all -- --check - clean
• ✅ npm run lint (frontend) - clean
• ✅ npm run format:check (frontend) - clean
• ✅ npm run lint (backend) - clean
• ✅ npm run format:check (backend) - clean

Type of Change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• All linting and formatting checks pass locally
• CI/CD pipeline is configured and tested

Note: This is a CI/CD infrastructure change (tooling/chore) adds automated
linting with no changes to application behaviour.

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@cyber-excel10 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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[ayomideadeniran]

@cyber-excel10 Resolve Merge conflict then i can review.

[ayomideadeniran]

@cyber-excel10 Please re-clone the repo and re-clone your current PR. The codebase has undergone significant structural and formatting changes for better stability and health.

[ayomideadeniran]

Impressive.

[cyber-excel10]

Impressive.

Thank You