feat: add Docker setup for documentation site

- Dockerfile.docs for building docs container
- nginx.conf for serving static Starlight site
- docker-compose.yml updated with docs service (--profile docs)
- Updated docs installation/deployment pages

docs/src/content/docs/deployment/docker.mdx

@@ -91,3 +91,20 @@ DATABASE_URL="postgresql://user:pass@host:5432/deardiary"
 ### Backup
 
 Regularly backup `./data/` directory.
+
+## Documentation Site
+
+Run the documentation site with Docker:
+
+```bash
+# Start just the docs site
+docker compose --profile docs up -d
+
+# Access at http://localhost:4000
+```
+
+Build the docs Docker image separately:
+
+```bash
+docker build -f Dockerfile.docs -t deardiary-docs .
+```

docs/src/content/docs/getting-started/installation.mdx

@@ -47,6 +47,17 @@ Change these credentials immediately after first login!
 |---------|------|-------------|
 | App | 8080 | Main application (nginx) |
 | API | 3000 | Backend API (internal) |
+| Docs | 4000 | Documentation site (optional, run with `--profile docs`) |
+
+## Documentation Site
+
+Run the documentation site separately:
+
+```bash
+docker compose --profile docs up -d
+```
+
+Access at `http://localhost:4000`
 
 ## Data Storage