Fix registerForActivityResult type inference in DocumentUploadDialog

- Remove explicit type annotation on lambda parameter to allow compiler inference
- Let OpenDocument() contract infer Uri? type from ActivityResultContract
- Resolves: 'Not enough information to infer type argument for I'

Author: claude

app/src/main/java/com/kharagedition/tibetankeyboard/chat/DocumentUploadDialog.kt

@@ -44,7 +44,7 @@ class DocumentUploadDialog(
 
     private val filePickerRequest = registerForActivityResult(
         androidx.activity.result.contracts.ActivityResultContracts.OpenDocument()
-    ) { uri: Uri? ->
+    ) { uri ->
         uri?.let {
             selectedFileUri = it
             updateFileDisplay(it)