fix(docker): single container (caddy+node), ESM adapters fix blank page

Docker: moved all docker files to docker/ tree (was conflated with
upstream Dockerfile at root + server/Dockerfile). Single container now:
caddy (front, serves static + proxies /api /ws) + node backend (internal
:4001). Node never exposed. entrypoint.sh runs both. Compose: one service.

Blank page root cause: storage adapters had inconsistent module systems.
firebase.js = ESM (export). ws.js + memory.js = CJS (module.exports).
CRA prod build = ESM strict -> CJS runtime crash, blank root. Dev mode
lenient, masked bug. First ws prod build (docker) = first exposure.
Never dev/prod split intended; just inconsistency from M2 era.

Fix: all adapters ESM. ws.js lazy-loads 'ws' pkg via dynamic import()
(Node/jest only; browser uses global WebSocket). index.js static
imports. server jest: added babel.config.js (preset-env, node target)
to transform ESM for jest.

Test: src/tests/StorageEsm.test.js — 4 tests grep all adapters for
module.exports / require(). Regression guard catches CJS leak.

Verified: docker page renders (root 4534 chars, UI visible).
server 24 green, shared 90 green, FE ESM 4 green.

docker/docker-compose.yml

@@ -0,0 +1,22 @@
+# docker/docker-compose.yml — single container: caddy (front) + node (back).
+# Usage (from repo root):
+#   docker compose -f docker/docker-compose.yml up --build
+services:
+  app:
+    build:
+      context: ..
+      dockerfile: docker/Dockerfile
+      args:
+        - REACT_APP_TRACKER_APP_ID=${TRACKER_APP_ID:-ttrpg-initiative-tracker-default}
+    image: ttrpg-app:local
+    ports:
+      - "${PORT:-8080}:80"
+    volumes:
+      - app-data:/data
+    environment:
+      - DB_PATH=/data/tracker.sqlite
+      - PORT=4001
+    restart: unless-stopped
+
+volumes:
+  app-data: