feat: initialize newsletter project with IMAP email processing and Discord integration

- Add Cargo.toml for project dependencies
- Create Dockerfile for building and running the application
- Add docker-compose configuration for service management
- Implement email monitoring and processing in main.rs
- Parse emails and send notifications to Discord
- Include configuration file for IMAP and Discord settings

.github/workflows/main.yml

@@ -0,0 +1,53 @@
+name: ci
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - 'v*'
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set version
+        run: |
+          if [[ "${GITHUB_REF}" == refs/heads/main ]]; then
+            echo "RELEASE_VERSION=latest" >> $GITHUB_ENV
+          else
+            echo "RELEASE_VERSION=${GITHUB_REF#refs/tags/v}" >> $GITHUB_ENV
+          fi
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+          tags: |
+            ghcr.io/imnyang/newsletter:latest
+            ghcr.io/imnyang/newsletter:${{ env.RELEASE_VERSION }}
+
+      - name: Create GitHub Release
+        if: startsWith(github.ref, 'refs/tags/')
+        uses: softprops/action-gh-release@v2
+        with:
+          tag_name: ${{ github.ref_name }}
+          name: Release ${{ github.ref_name }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}