v1.0.60: skip remote directories in sync + reduce concurrency to 2

- Filter out isDirectory entries from remoteFiles so remote folders are
  never treated as files to sync (fixes phantom-directory 'Partial ✗5' status)
- Lower Semaphore from 4 → 2 to reduce concurrent SFTP sessions and
  avoid hitting server session limits

app/src/main/kotlin/com/syncflow/domain/sync/SyncEngine.kt

@@ -77,6 +77,7 @@ class SyncEngine @Inject constructor(
         val accessor = makeAccessor(pair.localPath)
         var knownStates = fileStateDao.getForPair(pair.id).associateBy { it.relativePath }
         val remoteFiles = provider.listFiles(pair.remotePath).getOrThrow()
+            .filter { !it.isDirectory }  // skip remote directories — they are not sync targets
             .associateBy { it.path.removePrefix(pair.remotePath).trimStart('/') }
         val localFiles = accessor.walkFiles(pair)
 
@@ -93,7 +94,7 @@ class SyncEngine @Inject constructor(
 
         val allPaths = (localFiles.keys + remoteFiles.keys + knownStates.keys).toSet()
         val hasPriorSyncState = knownStates.isNotEmpty()
-        val semaphore = Semaphore(4)
+        val semaphore = Semaphore(2)  // limit concurrency to be gentle on the server
         val uploadedAtomic = AtomicInteger(0)
         val downloadedAtomic = AtomicInteger(0)
         val deletedAtomic = AtomicInteger(0)