v1.3.1 - Multi-Device Sync Fix + Performance + Restore Bug Fix

🔧 Fixed:
- Multi-device JSON sync now works (thanks Thomas!)
- Restore from Server skipped files (timestamp bug)
- No duplicate downloads
- First MD sync after export now fast

⚡ Performance:
- JSON sync: 12-14s → 2-3s
- Hybrid timestamp + E-Tag optimization
- Matches Markdown sync speed

✨ New:
- Sync status UI in MainActivity
- Content-based MD import
- Debug logging improvements
- SyncStateManager for sync coordination

🔧 Technical:
- Clear lastSyncTimestamp on restore
- Clear E-Tag caches on restore
- E-Tag refresh after upload
- Fixed timestamp update after MD export

android/app/src/main/res/layout/item_note.xml

@@ -64,7 +64,7 @@
                 android:layout_height="18dp"
                 android:layout_gravity="center_vertical"
                 android:src="@android:drawable/ic_popup_sync"
-                android:tint="?attr/colorPrimary"
+                app:tint="?attr/colorPrimary"
                 android:contentDescription="@string/sync_status" />
 
         </LinearLayout>