chore: Update SDK to fork in CrossPoint org (#1836)

## Summary

Update the Open X4 SDK to point to the CrossPoint organization fork.
This allows us to take SDK changes without being blocked on the upstream
repository.

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**NO**_

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "open-x4-sdk"]
 	path = open-x4-sdk
-	url = https://github.com/open-x4-epaper/community-sdk.git
+	url = https://github.com/crosspoint-reader/community-sdk.git