Add automated database schema diagram generation

.github/workflows/schema-diagram.yml

@@ -0,0 +1,72 @@
+---
+name: Generate Database Schema Diagram
+
+on: # yamllint disable-line rule:truthy
+  workflow_dispatch: null
+  push:
+    branches:
+      - main
+    paths:
+      - "backend/app/models/**"
+      - ".github/workflows/schema-diagram.yml"
+  pull_request:
+    branches:
+      - main
+    paths:
+      - "backend/app/models/**"
+      - ".github/workflows/schema-diagram.yml"
+
+permissions:
+  contents: read
+
+jobs:
+  generate-schema-diagram:
+    name: Generate Schema Diagram
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        # v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
+        with:
+          persist-credentials: false
+
+      - name: Setup Python
+        # v6
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405
+        with:
+          python-version: "3.14"
+          cache: "pip"
+          cache-dependency-path: backend/requirements.txt
+
+      - name: Install backend dependencies
+        run: .github/scripts/install-backend-deps.sh
+
+      - name: Create database with schema
+        working-directory: ./backend
+        run: |
+          mkdir -p data
+          python -c "from app.models import init_db; init_db(); print('Database initialized with schema')"
+
+      - name: Generate schema diagram with SchemaCrawler
+        # v16.22.2
+        uses: >
+          schemacrawler/SchemaCrawler-Action@83d8b85e5623e7a6d7fb1b33ad2ee53f8e36fa41
+        with:
+          schemacrawler-version: "16.22.2"
+          entrypoint: /schemacrawler.sh
+          args: >
+            --server=sqlite
+            --database=./backend/data/hadiscover.db
+            --info-level=standard
+            --command=schema
+            --output-format=png
+            --output-file=database-schema.png
+
+      - name: Upload schema diagram as artifact
+        # v4
+        uses: actions/upload-artifact@ea054a5b3e5eb6d1e9c84e0c37291e9c0c6ddfec
+        with:
+          name: database-schema-diagram
+          path: database-schema.png
+          retention-days: 90

ARCHITECTURE.md

@@ -79,6 +79,8 @@ SQLite Database ←→ GitHub API
 
 ## Database Schema
 
+> **Note**: A visual schema diagram is automatically generated by the [schema-diagram workflow](.github/workflows/schema-diagram.yml) whenever database models change. The diagram is available as a build artifact in GitHub Actions.
+
 ### repositories
 
 ```sql