Add GitHub Actions workflows for Copilot setup and Continuous Integration with Yarn support

.github/workflows/ci.yml

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+name: Continuous Integration
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    environment: CI
+
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@v2
+        with:
+          egress-policy: audit
+
+      - name: Checkout Source
+        uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Enable Corepack and Enforce Yarn Version
+        run: |
+          corepack enable
+          yarn set version 4.9.2
+
+      - name: Install Dependencies
+        run: yarn install
+
+      - name: Run Linter
+        run: yarn lint
+
+      - name: Build Project
+        run: yarn build
+
+      - name: Run Tests
+        run: yarn test

.github/workflows/copilot-setup-steps.yml

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+name: "Copilot Setup Steps"
+
+# Automatically run the setup steps when they are changed to allow for easy validation, and
+# allow manual testing through the repository's "Actions" tab
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+
+    # Set the permissions to the lowest permissions possible needed for your steps.
+    # Copilot will be given its own token for its operations.
+    permissions:
+      # If you want to clone the repository as part of your setup steps, for example to install dependencies, you'll need the `contents: read` permission. If you don't clone the repository in your setup steps, Copilot will do this for you automatically after the steps complete.
+      contents: read
+
+    # You can define any steps you want, and they will run before the agent starts.
+    # If you do not check out your code, Copilot will do this for you.
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v5
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+          cache: "yarn"
+
+      - name: Enable Corepack
+        run: corepack enable
+
+      - name: Install JavaScript dependencies
+        run: yarn install --immutable