chore: add database diagram generator

README.md

@@ -96,6 +96,24 @@ cd frontend
 npm run build
 ```
 
+## Database Diagram
+
+Start PostgreSQL, then generate a local schema diagram:
+
+```bash
+./scripts/generate-db-diagram.sh
+```
+
+The script writes an HTML viewer, SVG, PNG, and Graphviz source under:
+
+```txt
+.artifacts/db-diagrams/
+```
+
+Use `DATABASE_URL`, `PGPASSWORD`, or `~/.pgpass` to provide local database credentials.
+When using the repository infrastructure script, the diagram script can read from the
+running `socialize-postgres` container directly.
+
 ## Agentic Workflow
 
 Start here: