Fail safely instead of degrading silently in spotify_to_plex startup

- Exit with a clear error if the /app/config migration fails, rather than
  continuing to run against the non-persistent source directory (user
  changes would otherwise silently vanish on the next restart).
- Exit with a clear error if /app is missing instead of swallowing a
  broken upstream image layout with `|| true`.

Addresses further review feedback from PR #2816.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NZTfSk3GQRU7oD85TnjsmW

spotify_to_plex/rootfs/etc/cont-init.d/99-run.sh

@@ -11,7 +11,7 @@ if [ -d /app/config ] && [ ! -L /app/config ]; then
     if cp -rn /app/config/. "$CONFIG_TARGET/"; then
         rm -rf /app/config
     else
-        bashio::log.error "Failed to migrate /app/config to $CONFIG_TARGET; leaving original config in place"
+        bashio::exit.nok "Failed to migrate /app/config to $CONFIG_TARGET; refusing to start with a non-persistent config"
     fi
 fi
 
@@ -36,5 +36,5 @@ if [ -z "${ENCRYPTION_KEY:-}" ]; then
 fi
 
 # Hand off to the upstream supervisord (web + scraper + scheduler)
-cd /app || true
+cd /app || bashio::exit.nok "Cannot find /app (upstream image layout may have changed)"
 exec /docker-entrypoint.sh supervisord -n -c /etc/supervisor/conf.d/supervisord.conf