Dockerize Django app with dev/beta/prod env config and uv (#6)

## Summary

- Containerize the Django app with Docker and docker-compose (dev + production)
- Refactor settings into `dev` / `beta` / `prod` environments driven by environment variables
- Connect to PostgreSQL via `DATABASE_URL` or `DB_*` vars
- Migrate package management from pip to uv (`pyproject.toml`, `uv.lock`)
- Split Gitea workflows: PRs run unit tests only; pushes to `master` run tests, Docker validation, and deploy
- Update deploy script to rsync code, preserve server `.env`, validate config, and run Docker compose

Closes #4

## Test plan

- [x] `uv run python manage.py test` passes locally (10/10)
- [x] `DJANGO_ENV=beta` and `DJANGO_ENV=prod` load with correct logging levels
- [x] `scripts/validate-env.sh` rejects missing production variables
- [ ] `docker compose up --build` starts app + Postgres locally
- [ ] Containerized unit tests pass in CI Docker job
- [ ] Server `.env` created from `.env.prod.example` before first production deploy
- [ ] CI workflow runs on this PR (tests only, no deploy)

Reviewed-on: #6

.env.prod.example

@@ -0,0 +1,41 @@
+# Server-side production environment file.
+# Copy to /home/westfarn/Documents/django_live_sites/Company_Site/.env
+# This file is NOT deployed from git — rsync excludes .env so server values persist.
+
+# Environment level: dev | beta | prod
+DJANGO_ENV=prod
+DJANGO_DEBUG=false
+DJANGO_SECRET_KEY=replace-with-a-long-random-secret
+DJANGO_ALLOWED_HOSTS=aimloperations.com,www.aimloperations.com
+
+# Logging (optional override; defaults: dev=DEBUG, beta=INFO, prod=WARNING)
+# DJANGO_LOG_LEVEL=WARNING
+
+# PostgreSQL — DATABASE_URL is used by Django; DB_* are used by the db container.
+DATABASE_URL=postgres://company_site:replace-db-password@db:5432/company_site
+DB_NAME=company_site
+DB_USER=company_site
+DB_PASSWORD=replace-db-password
+
+# Analytics
+TIANJI_ENABLED=true
+TIANJI_TRACKER_URL=https://tianji.aimloperations.com/tracker.js
+TIANJI_WEBSITE_ID=replace-with-production-website-id
+
+# reCAPTCHA
+RECAPTCHA_PUBLIC_KEY=replace-with-production-public-key
+RECAPTCHA_PRIVATE_KEY=replace-with-production-private-key
+
+# Email (SMTP2GO)
+EMAIL_HOST=mail.smtp2go.com
+EMAIL_HOST_USER=replace-with-smtp-user
+EMAIL_HOST_PASSWORD=replace-with-smtp-password
+EMAIL_PORT=2525
+EMAIL_USE_TLS=true
+
+# Gunicorn
+GUNICORN_WORKERS=2
+GUNICORN_BIND=0.0.0.0:8000
+
+# Host port exposed by docker-compose.prod.yml
+WEB_PORT=8000