tech: add GitHub Actions CI workflow

[lucasgauthier]

Problem

No GitHub Actions CI workflow (for lint, typecheck, test)

Solution

Add GitHub Actions CI workflow

We also update .vscode/settings.json to support ESLint on github-actions-workflow files

[Copilot]

Pull request overview

Adds a baseline GitHub Actions CI pipeline so pushes/PRs to main automatically run lint, typecheck, and tests, and updates VS Code ESLint validation to include GitHub Actions workflow files.

Changes:

• Add a new .github/workflows/ci.yml workflow that runs pnpm lint, pnpm typecheck, and pnpm test.
• Update .vscode/settings.json so ESLint validates github-actions-workflow files.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
.vscode/settings.json	Enables ESLint validation for GitHub Actions workflow files in VS Code.
.github/workflows/ci.yml	Introduces CI jobs for linting, typechecking, and running tests on main pushes and PRs.

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