🐛(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>

src/backend/impress/settings.py

@@ -528,6 +528,9 @@ class Base(Configuration):
     )
 
     # AI service
+    AI_FEATURE_ENABLED = values.BooleanValue(
+        default=False, environ_name="AI_FEATURE_ENABLED", environ_prefix=None
+    )
     AI_API_KEY = values.Value(None, environ_name="AI_API_KEY", environ_prefix=None)
     AI_BASE_URL = values.Value(None, environ_name="AI_BASE_URL", environ_prefix=None)
     AI_MODEL = values.Value(None, environ_name="AI_MODEL", environ_prefix=None)