Dockerize Django app with dev/beta/prod env config and uv.

Replace hardcoded settings with environment-driven config, add Docker
compose for local and production deploys, migrate from pip to uv, and
split Gitea workflows so PRs run tests only while master pushes deploy.

.gitea/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: self-hosted
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install uv
+        run: |
+          curl -LsSf https://astral.sh/uv/install.sh | sh
+          echo "$HOME/.local/bin" >> "$GITHUB_PATH"
+
+      - name: Install dependencies
+        run: uv sync --frozen
+
+      - name: Run unit tests
+        env:
+          DJANGO_ENV: dev
+          DJANGO_SECRET_KEY: test-secret-key
+        run: |
+          cd company_site
+          uv run python manage.py test