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

.gitea/workflows/ci.yml

@@ -0,0 +1,27 @@
+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: |
+          uv run python manage.py test