v1.0.53: block storage-root sync paths

Android 11+ denies writes to /storage/emulated/0 directly. SyncEngine
now catches this early and returns FAILED with an actionable message
instead of silently logging PARTIAL. LocalBrowserDialog disables the
Select button at the storage root with an inline warning.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/src/main/kotlin/com/syncflow/ui/browser/LocalBrowserDialog.kt

@@ -263,22 +263,32 @@ fun LocalBrowserDialog(
                 }
 
                 // ── Select button ────────────────────────────────────────────
+                val isStorageRoot = currentPath.absolutePath == STORAGE_ROOT.absolutePath
                 Surface(tonalElevation = 4.dp, modifier = Modifier.fillMaxWidth()) {
                     Column {
-                    Button(
-                        onClick = { onSelect(currentPath.absolutePath) },
-                        modifier = Modifier
-                            .fillMaxWidth()
-                            .padding(start = 16.dp, top = 12.dp, end = 16.dp, bottom = 12.dp)
-                            .height(52.dp),
-                        shape = RoundedCornerShape(14.dp),
-                    ) {
-                        Icon(Icons.Default.CheckCircle, null, Modifier.size(20.dp))
-                        Spacer(Modifier.width(8.dp))
-                        Text("Select  \"$currentFolderName\"",
-                            style = MaterialTheme.typography.titleSmall, fontWeight = FontWeight.SemiBold)
-                    }
-                    Spacer(Modifier.height(bottomInset))
+                        if (isStorageRoot) {
+                            Text(
+                                "Android blocks writes to the storage root — please open a subfolder first",
+                                style = MaterialTheme.typography.bodySmall,
+                                color = MaterialTheme.colorScheme.error,
+                                modifier = Modifier.padding(horizontal = 20.dp, vertical = 8.dp),
+                            )
+                        }
+                        Button(
+                            onClick = { onSelect(currentPath.absolutePath) },
+                            enabled = !isStorageRoot,
+                            modifier = Modifier
+                                .fillMaxWidth()
+                                .padding(start = 16.dp, top = 4.dp, end = 16.dp, bottom = 12.dp)
+                                .height(52.dp),
+                            shape = RoundedCornerShape(14.dp),
+                        ) {
+                            Icon(Icons.Default.CheckCircle, null, Modifier.size(20.dp))
+                            Spacer(Modifier.width(8.dp))
+                            Text("Select  \"$currentFolderName\"",
+                                style = MaterialTheme.typography.titleSmall, fontWeight = FontWeight.SemiBold)
+                        }
+                        Spacer(Modifier.height(bottomInset))
                     }
                 }
             }