Implement v1 URL shortener (Bearer API, public 302, landing, CI) (#2)

## Summary

- Standalone Django 6 shortener: Bearer `/api/links/` (create/list/detail/disable) and public `GET /<code>` 302
- Host split, target-host allowlist, named rotatable tokens; `short_url` from `PUBLIC_SHORT_URL`
- Landing page, DEBUG-only `/debug/` mint form, Django admin
- Docker/compose (host **8005**), Gitea CI like monica_site (PR tests, beta on merge, prod button)
- Caller contract in `API.md`

Closes #1. Infra follow-up: [server-infra#22](ai_ml_operations/server-infra#22).

## Test plan
- [ ] `cd site && uv run python manage.py test`
- [ ] `docker compose up --build` → http://127.0.0.1:8005/
- [ ] `POST /api/links/` with `Bearer monica:dev-only-token` → 201
- [ ] `GET /<code>` → 302 to allowlisted https URL
- [ ] No Bearer → 401; non-allowlisted host → 400
- [ ] `/debug/` only when `DEBUG=true`

Reviewed-on: #2

.gitea/workflows/ci.yml

@@ -0,0 +1,36 @@
+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
+          DATABASE_URL: ""
+          DB_HOST: ""
+          SHORTENER_API_TOKENS: monica:dev-only-token
+          PUBLIC_SHORT_URL: https://go.mkdrealtor.com
+          SHORT_PUBLIC_HOSTS: go.mkdrealtor.com
+          SHORT_API_HOSTS: testserver,localhost,127.0.0.1
+          SHORT_ALLOWED_HOSTS: mkdrealtor.com
+          CLICK_IP_PEPPER: test-pepper
+        run: |
+          cd site
+          uv run python manage.py test