chore(immich): drop the IMMICH_URL hook

A deployment no longer suggests an address for the first server: every
address is each account's own and is typed in the app, so the field opens
blank with a placeholder. The env var, its compose passthrough, the example
line and the `defaultUrl` field that carried it are all gone; the backend's
config route now answers with the saved list alone.

docker/.env.example

@@ -23,10 +23,3 @@ SMTP_PASS=
 # What the mail says it is from. Defaults to SMTP_USER, then a noreply address.
 SMTP_FROM=
 SMTP_SECURE=
-
-# Immich, as a second photo source beside the folders on disk in LIBRARY. This is
-# only the address the "add an Immich server" dialog starts with — the key is
-# each account's own, typed in the app and kept in the database (never in the
-# browser, never in this file). Leave it empty and the field starts blank; the
-# "add Immich" button is there either way.
-IMMICH_URL=https://photos.labz.io.vn