LAN admin on 10.0.0.128 plus quick campaign mint form (#12)

Closes #11.

## Summary
- Serve Django admin on LAN IP `10.0.0.128` (not `piha.li`). Compose now publishes `0.0.0.0:8005` and passes `SHORT_ADMIN_HOSTS` into the container.
- Admin index has a campaign mint form: domain, campaign, source, metric. Save builds `https://{domain}/?utm_campaign=&utm_source=&utm_medium=` (metric) and shows a copyable short URL.
- Public `/admin/` on `piha.lc` / `piha.li` stays 404.

## Test plan
- [ ] `cd site && uv run python manage.py test`
- [ ] Recreate compose (`docker compose up --build`) so `WEB_BIND` / `SHORT_ADMIN_HOSTS` take effect
- [ ] From another LAN machine: `http://10.0.0.128:8005/admin/` (staff login) shows the mint form
- [ ] Save a link for an allowlisted domain, copy the short URL, confirm it 302s
- [ ] `https://piha.li/admin` still 404

Reviewed-on: #12

docker-compose.yml

@@ -17,19 +17,20 @@ services:
   web:
     build: .
     ports:
-      - "127.0.0.1:8005:8000"
+      - "${WEB_BIND:-0.0.0.0}:8005:8000"
     volumes:
       - ./site:/app/site
     environment:
       DJANGO_ENV: ${DJANGO_ENV:-dev}
       DJANGO_SECRET_KEY: ${DJANGO_SECRET_KEY:-dev-only-change-me}
       DJANGO_DEBUG: ${DJANGO_DEBUG:-true}
-      DJANGO_ALLOWED_HOSTS: ${DJANGO_ALLOWED_HOSTS:-localhost,127.0.0.1,0.0.0.0,web,url-shortener}
+      DJANGO_ALLOWED_HOSTS: ${DJANGO_ALLOWED_HOSTS:-localhost,127.0.0.1,0.0.0.0,web,url-shortener,10.0.0.128}
       DATABASE_URL: ${COMPOSE_DATABASE_URL:-postgres://url_shortener:url_shortener@db:5432/url_shortener}
       SHORT_DOMAIN: ${SHORT_DOMAIN:-localhost:8005}
       PUBLIC_SHORT_URL: ${PUBLIC_SHORT_URL:-http://127.0.0.1:8005}
       SHORT_PUBLIC_HOSTS: ${SHORT_PUBLIC_HOSTS:-piha.lc}
       SHORT_API_HOSTS: ${SHORT_API_HOSTS:-localhost,127.0.0.1,0.0.0.0,web,url-shortener}
+      SHORT_ADMIN_HOSTS: ${SHORT_ADMIN_HOSTS:-localhost,127.0.0.1,10.0.0.128}
       SHORTENER_API_TOKENS: ${SHORTENER_API_TOKENS:-monica:dev-only-token}
       SHORT_ALLOWED_HOSTS: ${SHORT_ALLOWED_HOSTS:-mkdrealtor.com,aimloperations.com}
       SHORT_CODE_LENGTH: ${SHORT_CODE_LENGTH:-6}