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/deploy.yml

@@ -0,0 +1,45 @@
+name: Deploy SCHA
+
+# Runs after Unit Tests completes on master. Direct pushes only (not PRs).
+on:
+  workflow_run:
+    workflows: [Unit Tests]
+    types: [completed]
+    branches: [master]
+
+jobs:
+  docker:
+    if: gitea.event.workflow_run.conclusion == 'success' && gitea.event.workflow_run.event == 'push'
+    runs-on: self-hosted
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ gitea.event.workflow_run.head_sha }}
+
+      - name: Build Docker image
+        run: docker compose build
+
+      - name: Run containerized tests
+        run: |
+          docker compose up -d db
+          docker compose run --rm --entrypoint "" \
+            -e DJANGO_ENV=dev \
+            -e DJANGO_SECRET_KEY=test-secret-key \
+            -e DATABASE_URL=postgres://scha:scha@db:5432/scha \
+            web uv run python manage.py test
+          docker compose down
+
+  deploy:
+    if: gitea.event.workflow_run.conclusion == 'success' && gitea.event.workflow_run.event == 'push'
+    runs-on: self-hosted
+    needs: docker
+    env:
+      SERVER_INFRA_ROOT: /home/westfarn/Documents/repos/server-infra
+    steps:
+      - name: Deploy scha prod
+        run: |
+          "$SERVER_INFRA_ROOT/scripts/deploy.sh" \
+            --app scha \
+            --env prod \
+            --ref "${{ gitea.event.workflow_run.head_sha }}"