Add CI Build & Lint Checks for Solidity

[jhelison]

Is your feature request related to a problem? Please describe.
Currently, contributions aren’t automatically checked for syntax errors, formatting, or unit test failures.

Describe the solution you'd like
Configure GitHub Actions to run standard Solidity checks on PRs:

• solhint for linting
• prettier-plugin-solidity for formatting
• hardhat test for basic tests

Describe alternatives you've considered
Manual local testing, but this doesn’t ensure consistency.

Additional context
Refer to similar repos like the KiiChain core or EVM starter templates.