Add Docker packaging and Gitea Actions CI/CD pipeline.

Containerize the app for local and production deploys, and publish images
to the Gitea container registry on main pushes and version tags.

Co-authored-by: Cursor <cursoragent@cursor.com>

docker-compose.prod.yml

@@ -0,0 +1,28 @@
+# Production compose: pull the image built by Gitea Actions instead of building locally.
+#
+#   docker login gitea.scoutitsystems.com
+#   IMAGE_TAG=latest docker compose -f docker-compose.prod.yml up -d
+#
+# Set IMAGE_TAG to a release tag (e.g. v0.1.0) or sha-abc1234 from CI.
+
+services:
+  app:
+    image: gitea.scoutitsystems.com/woogi/conflict-checker:${IMAGE_TAG:-latest}
+    ports:
+      - "${PORT:-8099}:8099"
+    env_file:
+      - backend/.env
+    environment:
+      APP_BASE_URL: ${APP_BASE_URL:-http://localhost:8099}
+    volumes:
+      - uploads:/app/backend/uploads
+      - outputs:/app/backend/outputs
+      - llm_cache:/app/backend/.llm_cache
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
+    restart: unless-stopped
+
+volumes:
+  uploads:
+  outputs:
+  llm_cache: