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.

docker-compose.synology.yml

@@ -0,0 +1,30 @@
+# Compose para deploy no Synology DSM via Container Manager.
+# Puxa a imagem pré-construída do GHCR (sem build local no NAS).
+# Antes de subir, crie as pastas no NAS:
+#   mkdir -p /volume1/docker/reddit-media-collector/{downloads,data}
+#   cp config.yaml /volume1/docker/reddit-media-collector/config.yaml
+
+services:
+  collector:
+    image: ghcr.io/richardnixondev/reddit-media-collector:latest
+    container_name: reddit-media-collector
+    restart: unless-stopped
+    ports:
+      - "8000:8000"
+    volumes:
+      - /volume1/docker/reddit-media-collector/downloads:/app/downloads
+      - /volume1/docker/reddit-media-collector/data:/app/data
+      - /volume1/docker/reddit-media-collector/config.yaml:/app/config.yaml:ro
+    environment:
+      - RMC_TIMEZONE=America/Sao_Paulo
+      - RMC_DOWNLOAD_DIR=/app/downloads
+      - RMC_DB_PATH=/app/data/media.db
+      - RMC_SCHEDULER_DB=/app/data/scheduler.db
+      - RMC_SCHEDULER_CONFIG=/app/data/scheduler_config.yaml
+      # Ative HTTP Basic Auth se for expor pela internet (via Reverse Proxy DSM):
+      # - RMC_AUTH_USER=admin
+      # - RMC_AUTH_PASS=trocar-isto
+    # Se o DSM rodar o container como user diferente e der erro de permissão
+    # nas pastas, descomente abaixo apontando para o UID:GID dono de
+    # /volume1/docker/reddit-media-collector (descubra com `ls -ln`):
+    # user: "1026:100"