docs: Update PostgreSQL image version to 18-alpine and add default database password information for Docker Compose setup

Author: Lasim

development/backend/database/index.mdx

@@ -397,7 +397,7 @@ POSTGRES_SSL=true
 ```yaml
 services:
   postgres:
-    image: postgres:16-alpine
+    image: postgres:18-alpine
     environment:
       POSTGRES_DB: deploystack
       POSTGRES_USER: deploystack

development/backend/database/postgresql.mdx

@@ -265,7 +265,7 @@ This enables SSL with `rejectUnauthorized: false` for self-signed certificates.
 ```yaml
 services:
   postgres:
-    image: postgres:16-alpine
+    image: postgres:18-alpine
     environment:
       POSTGRES_DB: deploystack
       POSTGRES_USER: deploystack

self-hosted/docker-compose.mdx

@@ -44,6 +44,10 @@ Download the `docker-compose.yml` file to your working directory:
 curl -o docker-compose.yml https://raw.githubusercontent.com/deploystackio/deploystack/main/docker-compose.yml
 ```
 
+<Info>
+**Default Database Password**: The Docker Compose file uses a default PostgreSQL password (`deploystack`) for quick demos and local testing. For production or internet-exposed deployments, set a strong password via the `POSTGRES_PASSWORD` environment variable in your `.env` file.
+</Info>
+
 ### Step 2: Generate Encryption Secret
 
 DeployStack requires a secure encryption secret for protecting sensitive data like API keys and credentials.

self-hosted/quick-start.mdx

@@ -38,6 +38,10 @@ The fastest way to get DeployStack backend and frontend running with proper netw
     <Info>
     **Note**: This deploys the backend and frontend only. The satellite service must be deployed separately after completing the setup wizard (see [Satellite Service](#satellite-service) section below).
     </Info>
+
+    <Info>
+    **Default Database Password**: The Docker Compose file uses a default PostgreSQL password (`deploystack`) for quick demos and local testing. For production or internet-exposed deployments, add `POSTGRES_PASSWORD=your_secure_password` before the command.
+    </Info>
   </Step>
 
   <Step title="Access DeployStack">