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

site/shortener/settings/base.py

@@ -89,7 +89,7 @@ DEBUG = env_bool("DJANGO_DEBUG", False)
 
 allowed_hosts = env_list(
     "DJANGO_ALLOWED_HOSTS",
-    "localhost,127.0.0.1,0.0.0.0,testserver,web,url-shortener,piha.lc,beta.piha.li",
+    "localhost,127.0.0.1,0.0.0.0,testserver,web,url-shortener,10.0.0.128,piha.lc,beta.piha.li",
 )
 ALLOWED_HOSTS = allowed_hosts if allowed_hosts else ["*"]
 
@@ -185,7 +185,9 @@ SHORT_API_HOSTS = env_list(
     "localhost,127.0.0.1,0.0.0.0,testserver,web,url-shortener",
 )
 # Django admin — local/dev only. Never put the public short hostname here.
-SHORT_ADMIN_HOSTS = env_list("SHORT_ADMIN_HOSTS", "localhost,127.0.0.1")
+SHORT_ADMIN_HOSTS = env_list(
+    "SHORT_ADMIN_HOSTS", "localhost,127.0.0.1,10.0.0.128"
+)
 SHORTENER_API_TOKENS = parse_api_tokens(env("SHORTENER_API_TOKENS", "") or "")
 SHORT_ALLOWED_HOSTS = env_list(
     "SHORT_ALLOWED_HOSTS", "mkdrealtor.com,aimloperations.com"