🐛(frontend) conditionally render AI button in toolbar

Added a feature flag check to ensure the AIGroupButton is only rendered
when AI_FEATURE_ENABLED is explicitly set to "true". This prevents the
AI button from appearing when the feature is not configured or disabled.

Fixes #782

Signed-off-by: Matthias <matthias@universum.com>

env.d/development/common.dist

@@ -50,6 +50,7 @@ OIDC_REDIRECT_ALLOWED_HOSTS=["http://localhost:8083", "http://localhost:3000"]
 OIDC_AUTH_REQUEST_EXTRA_PARAMS={"acr_values": "eidas1"}
 
 # AI
+AI_FEATURE_ENABLED=true
 AI_BASE_URL=https://openaiendpoint.com
 AI_API_KEY=password
 AI_MODEL=llama