feat(deploy): publish image to GHCR and document Synology DSM setup

Add a release workflow that publishes a linux/amd64 image to
ghcr.io/richardnixondev/reddit-media-collector on every v* tag, plus a
ready-to-paste docker-compose for Synology Container Manager.

Persist scheduler state across container restarts by reading the DB and
config paths from RMC_SCHEDULER_DB / RMC_SCHEDULER_CONFIG (previously
written to /app, which is not a volume).

Drive-by fixes uncovered while smoke-testing the image:
- Dockerfile now copies README.md (required by pyproject) and drops the
  single-file VOLUME entry that breaks bind mounts; adds an OCI source
  label and a socket-based HEALTHCHECK so Container Manager reflects real
  liveness.
- src/web/app.py uses the new Starlette TemplateResponse signature so the
  index page does not 500 under fresh dependency pins.

.github/workflows/release.yml

@@ -0,0 +1,43 @@
+name: release
+
+on:
+  push:
+    tags:
+      - "v*"
+  workflow_dispatch:
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository_owner }}/reddit-media-collector
+          tags: |
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=raw,value=latest,enable=${{ github.ref_type == 'tag' }}
+
+      - 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