v1.0.54: ARCHIVE delete behavior + storage root upload-only allowance

New delete behavior option: "Archive deleted" — when a file is deleted
from the phone in a TWO_WAY pair, it moves to _Deleted/<path> on remote
instead of being permanently deleted from the backup.

Also allows storage root (/storage/emulated/0) for UPLOAD_ONLY pairs so
whole-phone backup syncs work; only blocks root when sync direction would
write files locally.

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

app/src/main/kotlin/com/syncflow/domain/model/SyncPair.kt

@@ -58,6 +58,7 @@ enum class ConflictStrategy(val label: String) {
 enum class DeleteBehavior(val label: String, val description: String) {
     MIRROR("Mirror deletions", "Delete on target when deleted on source"),
     KEEP("Keep deleted files", "Never delete — only add/update"),
+    ARCHIVE("Archive deleted", "Move files deleted from phone to _Deleted/ folder on remote"),
 }
 
 enum class ScheduleType(val label: String) {