feat: implement login screen UI and update project version to 2.1.6

scenes/ui/login_screen.tscn

@@ -316,6 +316,7 @@ horizontal_alignment = 1
 autowrap_mode = 2
 
 [node name="VersionLabel" type="Label" parent="." unique_id=481275614]
+visible = false
 layout_mode = 1
 anchors_preset = 3
 anchor_left = 1.0
@@ -331,4 +332,4 @@ grow_vertical = 0
 theme_override_colors/font_color = Color(0.6, 0.6, 0.6, 0.6)
 theme_override_font_sizes/font_size = 11
 text = "v2.1.2"
-horizontal_alignment = 2
+horizontal_alignment = 1