feat(open-notebook): put the podcast generator behind the guard chain

The service came up internal-only: UI on the LAN at 8502, API at 5056, both
published on every interface, with only its own shared password in front. That
put the episode library outside the fleet's auth chain and one port scan away
from anything on the network.

- Caddy: guarded vhost notebook.franksdank.cloud (Anubis -> Authentik; provider
  notebook-proxy, internal_host caddy:8017) plus the post-auth route to the
  published UI port. One upstream is enough, because the image's own Next.js
  layer rewrites /api/* to the FastAPI beside it — so the API needs no outward
  face at all, and 5056 moves to loopback, where only the deployer's health gate
  dials it.
- scripts/open-notebook.env: API_URL and CORS_ORIGINS become the single guarded
  origin. Left to itself the app auto-detects <host>:5055, the port seerr holds
  on this host; a LAN-origin API_URL would also take the browser around the
  guard chain, where its authenticated session does not ride.
- addn-hosts: the LAN A record. The homepage card goes live and links the vhost.
- Seam: the API origin is derived from whatever the Caddyfile routes to 8502, so
  renaming the vhost moves the test instead of leaving it blessing a stale name,
  and a new test proves the vhost hands the WHOLE request to Anubis.

shared/homepage/services.json

@@ -32,13 +32,13 @@
     "name": "open-notebook",
     "category": "user",
     "section": "AI",
-    "description": "Podcast generator — notes in, spoken episode out: script written by frank-zealot, voices rendered by frank-tts. No public route; LAN UI only once it is deployed.",
-    "url": "",
+    "description": "Podcast generator — notes in, spoken episode out: script written by frank-zealot, voices rendered by frank-tts. Guarded twice: Authentik at the edge, then its own login.",
+    "url": "http://notebook.franksdank.cloud",
     "docs": "",
     "probe": "127.0.0.1:8502",
     "method": "http",
-    "wip": "down",
-    "showLink": false,
+    "wip": false,
+    "showLink": true,
     "art": "/img/apps/mono-on.svg"
   },
   {