chore: remove Letterspace newsletter integration and all LETTERSPACE_* variables

DOCKER.md

@@ -53,9 +53,6 @@ docker run -d \
   -e PUBLIC_API_URL=https://api.pivoine.art \
   -e PUBLIC_URL=https://sexy.pivoine.art \
   -e PUBLIC_UMAMI_ID=your-umami-id \
-  -e LETTERSPACE_API_URL=https://api.letterspace.com/v1 \
-  -e LETTERSPACE_API_KEY=your-api-key \
-  -e LETTERSPACE_LIST_ID=your-list-id \
   sexy.pivoine.art:latest
 ```
 
@@ -117,9 +114,6 @@ docker-compose -f docker-compose.production.yml up -d --scale frontend=3
 | Variable | Description | Example |
 |----------|-------------|---------|
 | `PUBLIC_UMAMI_ID` | Umami analytics tracking ID | `abc123def-456` |
-| `LETTERSPACE_API_URL` | Letterspace API endpoint | `https://api.letterspace.com/v1` |
-| `LETTERSPACE_API_KEY` | Letterspace authentication key | `sk_live_...` |
-| `LETTERSPACE_LIST_ID` | Mailing list identifier | `list_abc123` |
 | `PORT` | Application port (inside container) | `3000` |
 | `HOST` | Host binding | `0.0.0.0` |
 | `NODE_ENV` | Node environment | `production` |
@@ -224,12 +218,12 @@ docker run -d \
 
 ```bash
 # Create secrets
-echo "your-api-key" | docker secret create letterspace_api_key -
+echo "your-db-password" | docker secret create db_password -
 
 # Deploy with secrets
 docker service create \
   --name sexy-pivoine-frontend \
-  --secret letterspace_api_key \
+  --secret db_password \
   -p 3000:3000 \
   sexy.pivoine.art:latest
 ```