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.

docker-compose.yml

@@ -0,0 +1,31 @@
+services:
+  db:
+    image: postgres:16-alpine
+    environment:
+      POSTGRES_DB: company_site
+      POSTGRES_USER: company_site
+      POSTGRES_PASSWORD: company_site
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U company_site -d company_site"]
+      interval: 5s
+      timeout: 5s
+      retries: 10
+      start_period: 10s
+
+  web:
+    build: .
+    ports:
+      - "8000:8000"
+    env_file:
+      - .env
+    environment:
+      DJANGO_ENV: dev
+      DATABASE_URL: postgres://company_site:company_site@db:5432/company_site
+    depends_on:
+      db:
+        condition: service_healthy
+
+volumes:
+  postgres_data: