docs: no update.sh until v1

Nothing has shipped, so there is nothing to update (the script itself was removed in
a152508). The v1.0 definition of done now requires update.sh written, reviewed and
tested on a real server; the admin guide says there are no releases yet.

Task: M11-T7

docs/admin-guide/maintenance.md

@@ -2,24 +2,8 @@
 
 ## Updating SelfPhoneNG
 
-When nobody is on a call, run:
-
-```sh
-./scripts/update.sh
-```
-
-It:
-
-1. pulls the latest code (`git pull --ff-only`);
-2. pulls newer PostgreSQL and Caddy images;
-3. rebuilds the api and Asterisk images;
-4. restarts what changed.
-
-Database changes apply by themselves when the api starts. **Calls in progress drop** if Asterisk is
-rebuilt. Make a backup first (**Settings → Backups → Back up now**).
-
-If `git pull` refuses because you changed files in the folder, put your changes somewhere else.
-Settings belong in the web app and `.env`, not in the code.
+SelfPhoneNG has no releases yet. How to update will be documented, with a tested update
+script, when version 1.0 ships.
 
 ### Asterisk security releases
 
@@ -35,7 +19,7 @@ docker compose up -d asterisk
 docker compose exec asterisk asterisk -rx "core show version"
 ```
 
-The next `update.sh` goes back to the version the code names.
+A later rebuild without `--build-arg` goes back to the version the code names.
 
 ## Backups