Dockerize scha + Gitea CI/CD auto-deploy via server-infra (#21)

## Summary
- Dockerize SCHA Wheaton (uv packaging, Dockerfile, compose, entrypoint) and move secrets/DB config to env-driven `scha/settings/`.
- Add Gitea Actions: unit tests on push/PR to `master`, auto-deploy on green master push via `server-infra/scripts/deploy.sh --app scha --env prod`.
- Prod compose uses shared external Postgres only (no bundled DB); control-node secret template at `.env.prod.example`.

Closes #19 (Part A). Depends on companion server-infra PR for catalog/host_apps registration.

## Test plan
- [ ] `uv sync --frozen` + `DJANGO_ENV=dev DJANGO_SECRET_KEY=test uv run python manage.py check`
- [ ] `docker compose build` succeeds locally
- [ ] `docker compose up` serves app against bundled Postgres
- [ ] `./scripts/validate-env.sh ~/Documents/secrets/scha/scha_prod.env` passes
- [ ] After merge + server-infra catalog live: push to master runs Unit Tests then Deploy

Reviewed-on: #21

Dockerfile

@@ -0,0 +1,28 @@
+FROM python:3.12-slim
+
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1 \
+    UV_COMPILE_BYTECODE=1 \
+    UV_LINK_MODE=copy \
+    UV_PROJECT_ENVIRONMENT=/app/.venv
+
+WORKDIR /app
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends libpq5 \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
+
+COPY pyproject.toml uv.lock ./
+RUN uv sync --frozen --no-dev
+
+COPY scha ./scha
+COPY schasite ./schasite
+COPY manage.py ./
+COPY scripts/docker-entrypoint.sh /entrypoint.sh
+RUN chmod +x /entrypoint.sh
+
+EXPOSE 8000
+
+ENTRYPOINT ["/entrypoint.sh"]