fix: remove unsupported priority key from YAML route definition

Symfony's YAML route loader does not support the priority key (only PHP config does).
Relying on vue_app being defined first in routes.yaml to ensure it is matched
before legacy controller routes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/routes.yaml

@@ -6,7 +6,6 @@ vue_app:
         req: ''
     requirements:
         req: "^(?!api/|legacy).*"
-    priority: 1
 
 controllers:
     resource: