Move Dockerfile, entrypoint.sh, docker-compose.yml to repo root

Komodo's build ran `docker build -f Dockerfile .` from inside docker/,
which set the build context to docker/ — a directory that contains neither
package.json nor a nested docker/entrypoint.sh, so both COPY steps failed.
Moving these three files to the repo root makes `docker build .` from the
repo root work with default Komodo settings (no per-build-tool config).

- Dockerfile: update COPY entrypoint.sh path (drops docker/ prefix)
- docker-compose.yml: build.context = . (drops dockerfile: override)
- README.md: docker compose build (drops -f docker/docker-compose.yml)

docker-compose.yml

@@ -0,0 +1,25 @@
+services:
+  electric-cherry:
+    build:
+      context: .
+    image: electric-cherry:latest
+    container_name: electric-cherry
+    restart: unless-stopped
+    ports:
+      - "3000:3000"
+    volumes:
+      # in prod (Komodo host), the game server tree is at /root/zombies
+      - /root/zombies:/root/zombies:rw
+      - /root/zombies/.electric-cherry:/data:rw
+    environment:
+      SHARED_SCRIPTS: /root/zombies/shared/scripts
+      SERVERS_ROOT: /root/zombies/t5
+      REL_DEST: runtime/plutonium/storage/t5/raw/scripts/sp
+      DB_PATH: /data/cherry.db
+      LEGACY_METADATA: /root/zombies/script_metadata.json
+      DEPLOY_KEEP_DAYS: "7"
+      KOMODO_ADDRESS: ${KOMODO_ADDRESS}
+      KOMODO_API_KEY: ${KOMODO_API_KEY}
+      KOMODO_API_SECRET: ${KOMODO_API_SECRET}
+      IW4M_ADDRESS: ${IW4M_ADDRESS}
+      IW4M_CLIENT_ID: ${IW4M_CLIENT_ID}