Use inline env vars in docker-compose, verify Docker build works

- docker-compose.yml: replace env_file with explicit environment block
  so all variables are passable directly (JWT_SECRET required, rest have defaults)
- Confirmed Docker image builds successfully

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -2,9 +2,19 @@ services:
   nanodrop:
     build: .
     ports:
-      - "3000:3000"
-    env_file:
-      - .env
+      - "${PORT:-3000}:3000"
+    environment:
+      PORT: "${PORT:-3000}"
+      HOST: "${HOST:-0.0.0.0}"
+      JWT_SECRET: "${JWT_SECRET}"
+      JWT_EXPIRY: "${JWT_EXPIRY:-7d}"
+      DB_PATH: "${DB_PATH:-./data/nanodrop.db}"
+      UPLOAD_DIR: "${UPLOAD_DIR:-./data/uploads}"
+      LOG_FILE: "${LOG_FILE:-./data/nanodrop.log}"
+      MAX_FILE_SIZE: "${MAX_FILE_SIZE:-104857600}"
+      BASE_URL: "${BASE_URL:-http://localhost:3000}"
+      COOKIE_SECURE: "${COOKIE_SECURE:-false}"
+      TRUST_PROXY: "${TRUST_PROXY:-false}"
     volumes:
       - nanodrop-data:/app/data
     restart: unless-stopped