feat: extend CI pipeline with contract checks and update contribution guidelines

[gabito1451]

Contribution Guidelines Update

I have successfully implemented the requested changes to extend the CI pipeline and update the contribution guidelines.

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Summary of Changes

1. Refactored Repository Structure

• Renamed the contract/ directory to contracts/ to ensure consistency with:
  • The project’s package.json workspaces configuration
  • Existing README.md instructions

---

2. Extended ci.yml Workflow

• Added a new contracts job that runs on every push and pull request
• Configured the job to:
  • Install the Rust toolchain with:
    • wasm32-unknown-unknown target
    • rustfmt component
  • Install the Stellar CLI
• Added steps to:
  • Run formatting checks:

    cargo fmt --check

  • Build the contract:

    stellar contract build

  • Run tests:

    cargo test

  • All commands are executed within the contracts/ directory

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3. Updated ci-cd.yml Workflow

• Replaced placeholder comments in the build-and-deploy job with actual build steps
• The job now:
  • Checks out the code
  • Sets up Node.js 20.x
  • Installs dependencies:

    npm ci

  • Builds both:
    • Frontend workspace
    • Backend workspace
• Maintained dependency on the validate-pr job

---

4. Updated CONTRIBUTING.md

• Added a dedicated section for contract contributors under "MUST RUN local checks", including:
  • Required prerequisites
  • Commands to run before submitting a PR
• Updated Branch Protection rules to include:
  • contracts as a required status check
  • Alongside:
    • lint-imports
    • build
    • type-check

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