Add Docker Compose setup for local runs

PHP 8.3 + Apache image serving public/ on port 8080, with pdo_sqlite and
mbstring built in. The container entrypoint applies migrations as www-data
before starting Apache; the SQLite database and generated JWT signing key
persist in a named "storage" volume. `docker compose up -d` is now the
primary way to run the project without a local PHP toolchain.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,18 @@
+services:
+  app:
+    build: .
+    image: php-todo-list
+    ports:
+      - "8080:80"
+    environment:
+      APP_DEBUG: "${APP_DEBUG:-false}"
+      # Leave blank to auto-generate a secret into the storage volume on first run.
+      JWT_SECRET: "${JWT_SECRET:-}"
+      JWT_TTL: "${JWT_TTL:-86400}"
+    volumes:
+      # Persists the SQLite database and the generated signing key across restarts.
+      - storage:/var/www/html/storage
+    restart: unless-stopped
+
+volumes:
+  storage: