integrate npm run build in CI workflows

[Nacho1499]

closes #27

Problem Statement:
Currently, there is no automated check to ensure that new code doesn't break the build process. Contributors have to manually verify builds, which can lead to broken code in the main branch.

PR Description:
This PR adds a GitHub Actions workflow (ci.yml) that automatically triggers on every pull request to main and develop.

Key Changes:

• Automated Build: Runs npm run build on every PR.
• Linting: Includes npm run lint to enforce code quality.
• Caching: Configured actions/setup-node with cache: 'npm' to speed up workflow execution.
• Reproducibility: Uses npm ci instead of npm install for consistent environments.

Verification:

• Workflow triggers on PR creation.
• Node.js environment sets up correctly (v20).
• Dependencies install successfully.
• npm run build completes without errors.

[Nacho1499]

"Refactored ThemeToggle to fix the CI linting errors properly.
Instead of just silencing the warning, I implemented lazy state initialization to prevent cascading renders and fixed a hook-placement issue found during the merge. The component is now more performant and the CI is good."

By fixing the code instead of ignoring the error, i have successfully:
Validated the CI setup: this proved the linting rules are active and enforcing standards.
Improved the codebase: i left the project better than you found it.

[Nacho1499]

[Nacho1499]

[Nacho1499]