added context warning

Author: soheimam

docs/mini-apps/features/Context.mdx

@@ -22,6 +22,11 @@ Context provides three essential data objects that shape your user experience:
 </Card>
 </CardGroup>
 
+<Warning>
+**Context is only available within the Base App client, not on the web.**
+If your mini app is accessed via a standard web browser, context data will not be provided. Design your app to gracefully handle the absence of context when running outside the Base App environment.
+</Warning>
+
 ## Why Context Matters
 
 Context enables you to create mini apps that feel native to their social environment and optimize for viral growth: