Rename the app service to landing-app to avoid a Dokploy network collision

Compose aliases a service to its own name on every network it joins,
including the shared external dokploy-network. A service named plain
"app" collided with another project's equally generic "app" on that
same network, so its containers started resolving "app" to this one
instead — breaking oauth-iam's PHP-FPM upstream whenever both stacks
were up together.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.env.production.example

@@ -4,7 +4,7 @@
 #   cp .env.production.example .env.production
 #   # fill in at least DB_PASSWORD below — docker-compose.yml refuses to
 #   # interpolate at all without it, even for the next command
-#   docker compose --env-file .env.production run --rm --no-deps app php artisan key:generate --show
+#   docker compose --env-file .env.production run --rm --no-deps landing-app php artisan key:generate --show
 #
 # Everything the containers need is here; docker-compose.yml sets the database,
 # cache, session and queue drivers itself so they cannot drift.