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/docker-compose.yml

@@ -23,11 +23,6 @@ services:
       SMTP_PASS: ${SMTP_PASS:-}
       SMTP_FROM: ${SMTP_FROM:-}
       SMTP_SECURE: ${SMTP_SECURE:-}
-      # Immich, offered as a second photo source in LIBRARY. This is only the
-      # address the "add an Immich server" dialog starts with: the URL and the
-      # key belong to each account, are typed in the app, and are stored in the
-      # users table. Empty simply means the field starts blank.
-      IMMICH_URL: ${IMMICH_URL:-}
     volumes:
       # SQLite (WAL) lives on the host so a rebuild never loses accounts.
       - ./data:/data