Add CI workflow with linting, type checking, and tests

Set up GitHub Actions to run on pushes and PRs to master branch.
Uses pnpm for package management. Salesforce contract tests use
credentials from GitHub secrets.

Author: pettinarip

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'pnpm'
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Run linter
+        run: pnpm run lint
+
+      - name: Run type check
+        run: pnpm run type-check
+
+      - name: Run tests
+        env:
+          SF_PROD_LOGIN_URL: ${{ secrets.SF_PROD_LOGIN_URL }}
+          SF_PROD_USERNAME: ${{ secrets.SF_PROD_USERNAME }}
+          SF_PROD_PASSWORD: ${{ secrets.SF_PROD_PASSWORD }}
+          SF_PROD_SECURITY_TOKEN: ${{ secrets.SF_PROD_SECURITY_TOKEN }}
+        run: pnpm test