refactor: Split CI workflows into separate jobs for better feedback and parallel execution

[TejInaco]

Currently, unit tests are bundled with the publication workflow, making it harder for developers to identify which check failed and slowing down feedback.

Separate GitHub Actions workflows into independent files:

tests.yml - Unit tests (vitest)
lint.yml - ESLint checks
format.yml - Prettier formatting validation
publish-to-gh-pages.yml - Keep as-is for deployment

[yashgoyal0110]

/assign

[egekorkan]

@TejInaco will be handling this one but thank you @yashgoyal0110 for volunteering!