CI : publication automatique de l'image Docker sur GHCR

- .github/workflows/docker-publish.yml : build + push de ghcr.io/r0m1k3/loki
  (linux/amd64, tags latest + sha, cache GHA) à chaque push sur main
- docker-compose.unraid.yml : utilise l'image préconstruite (plus de build/git
  sur Unraid, simple pull)
- README : instructions Unraid mises à jour (image GHCR, visibilité du package)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SVay7z3y7q2gEe54ByAE6N

.github/workflows/docker-publish.yml

@@ -0,0 +1,47 @@
+name: Publier l'image Docker (GHCR)
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  packages: write
+
+jobs:
+  build-push:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Connexion à GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Métadonnées (tags / labels)
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository }}
+          tags: |
+            type=raw,value=latest
+            type=sha,format=short
+
+      - name: Build & push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          platforms: linux/amd64
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max