feat(ci): add GHCR build workflow for intermediate versions

- Builds on every push to any branch and on tags
- Tags: branch-sha for branches (e.g. main-abc1234)
- Tags: semver for releases (e.g. v1.0.0, latest)
- Allows deploying intermediate versions to homelab

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vanadium23

.github/workflows/ghcr.yml

@@ -0,0 +1,61 @@
+name: Build and Push to GHCR
+
+on:
+  push:
+    branches:
+      - '**'
+    tags:
+      - 'v*'
+  workflow_dispatch:
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels)
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            # For tags: v1.0.0 -> v1.0.0, latest
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=raw,value=latest,enable=${{ startsWith(github.ref, 'refs/tags/') }}
+            # For branches: feature/foo -> feature-foo-sha, main -> main-sha
+            type=ref,event=branch,suffix=-{{sha}}
+            # For PRs: pr-123
+            type=ref,event=pr
+
+      - name: Build and push
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          build-args: |
+            KOMPANION_VERSION=${{ github.ref_name }}-${{ github.sha }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max