fix: remove SCRAPY_AUTH_USERS default from arty.yml

Removed default SCRAPY_AUTH_USERS value from arty.yml to ensure
credentials are only read from .env file (secrets).

This fixes login issues where the default placeholder value was
being used instead of actual credentials from .env.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

arty.yml

@@ -62,7 +62,6 @@ envs:
     SCRAPY_TRAEFIK_HOST: scrapy.pivoine.art
     SCRAPY_SCRAPYD_PORT: 6800
     SCRAPY_SCRAPYRT_PORT: 9080
-    SCRAPY_AUTH_USERS: admin:$$apr1$$changeme$$example
     # n8n
     N8N_TRAEFIK_ENABLED: true
     N8N_COMPOSE_PROJECT_NAME: n8n