Add dual-registry Docker deployment (GHCR + private registry)

- Update CI workflow to build separate backend/frontend images via matrix
- Push to both ghcr.io and registry.cklnet.com
- Add private registry login step with secret credentials
- Keep existing metadata-action tags and multi-platform builds
- Update CHANGELOG.md and docs/TODO.md

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
Agent-Logs-Url: https://github.com/christianlouis/pop_puller_to_gmail/sessions/05b6d21a-2397-4039-9c69-46db79ec11de

.github/workflows/ci.yml

@@ -12,8 +12,8 @@ on:
   workflow_dispatch:
 
 env:
-  REGISTRY: ghcr.io
-  IMAGE_NAME: ${{ github.repository }}
+  GHCR_REGISTRY: ghcr.io
+  PRIVATE_REGISTRY: registry.cklnet.com
 
 jobs:
   # ── Phase 1: Lint ──────────────────────────────────────────────────────
@@ -169,6 +169,14 @@ jobs:
       contents: read
       packages: write
 
+    strategy:
+      matrix:
+        include:
+          - context: ./backend
+            image_name: gmail-puller/backend
+          - context: ./frontend
+            image_name: gmail-puller/frontend
+
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
@@ -176,18 +184,28 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v4
 
-      - name: Log in to Container Registry
+      - name: Log in to GitHub Container Registry
         uses: docker/login-action@v3
         with:
-          registry: ${{ env.REGISTRY }}
+          registry: ${{ env.GHCR_REGISTRY }}
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
+      # Requires PRIVATE_REGISTRY_USERNAME and PRIVATE_REGISTRY_PASSWORD secrets
+      - name: Log in to private registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.PRIVATE_REGISTRY }}
+          username: ${{ secrets.PRIVATE_REGISTRY_USERNAME }}
+          password: ${{ secrets.PRIVATE_REGISTRY_PASSWORD }}
+
       - name: Extract metadata (tags, labels)
         id: meta
         uses: docker/metadata-action@v5
         with:
-          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          images: |
+            ${{ env.GHCR_REGISTRY }}/${{ github.repository_owner }}/${{ matrix.image_name }}
+            ${{ env.PRIVATE_REGISTRY }}/${{ matrix.image_name }}
           tags: |
             type=semver,pattern={{version}}
             type=semver,pattern={{major}}.{{minor}}
@@ -199,7 +217,7 @@ jobs:
         id: build-push
         uses: docker/build-push-action@v5
         with:
-          context: .
+          context: ${{ matrix.context }}
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}