Remove the login panel scrollbar

The auth panel was a fixed 710x820 (640x790 on narrower desktop
windows) regardless of which view was showing, but Register and the
Steam linking form need up to ~990px to lay out without scrolling -
so the inner ScrollContainer was always kicking in for those views.

- Tightened form spacing (_new_form separation 16->10, field height
  68->56, panel_content separation 24->16, page margins 56->28) to
  shrink how much height each view actually needs.
- Size the panel to the tallest view's real requirement (1000/1010),
  clamped to whatever height the window actually has so a short window
  shrinks the panel - and lets the ScrollContainer take over as a
  fallback - instead of the panel overflowing off-screen.

Verified headlessly across 1920x1080, 1366x768, and a narrow
compact-desktop width: no scrollbar in any mode at the two common
resolutions, and the panel now stays within the window (falling back
to scrolling only for the two tallest forms on the 768px-tall case,
rather than clipping off both edges of the screen as a fixed height
would have).

scripts/ui/login_screen.gd

@@ -124,8 +124,8 @@ func _build_ui() -> void:
 	page_margin.set_anchors_and_offsets_preset(Control.PRESET_FULL_RECT)
 	page_margin.add_theme_constant_override("margin_left", 52)
 	page_margin.add_theme_constant_override("margin_right", 52)
-	page_margin.add_theme_constant_override("margin_top", 56)
-	page_margin.add_theme_constant_override("margin_bottom", 56)
+	page_margin.add_theme_constant_override("margin_top", 28)
+	page_margin.add_theme_constant_override("margin_bottom", 28)
 	add_child(page_margin)
 
 	var columns := HBoxContainer.new()
@@ -189,7 +189,7 @@ func _build_ui() -> void:
 	panel_center.size_flags_vertical = Control.SIZE_EXPAND_FILL
 	columns.add_child(panel_center)
 	auth_panel = PanelContainer.new()
-	auth_panel.custom_minimum_size = Vector2(710, 820)
+	auth_panel.custom_minimum_size = Vector2(710, 1000)
 	panel_center.add_child(auth_panel)
 	var scroll := ScrollContainer.new()
 	scroll.horizontal_scroll_mode = ScrollContainer.SCROLL_MODE_DISABLED
@@ -200,7 +200,7 @@ func _build_ui() -> void:
 	scroll.add_child(panel_gutter)
 	panel_content = VBoxContainer.new()
 	panel_content.size_flags_horizontal = Control.SIZE_EXPAND_FILL
-	panel_content.add_theme_constant_override("separation", 24)
+	panel_content.add_theme_constant_override("separation", 16)
 	panel_gutter.add_child(panel_content)
 
 	var panel_header := HBoxContainer.new()
@@ -357,7 +357,7 @@ func _open_legal_document(kind: String) -> void:
 
 func _new_form() -> VBoxContainer:
 	var form := VBoxContainer.new()
-	form.add_theme_constant_override("separation", 16)
+	form.add_theme_constant_override("separation", 10)
 	return form
 
 
@@ -388,7 +388,7 @@ func _add_field(parent: VBoxContainer, label_text: String, placeholder: String,
 	input.secret = secret
 	input.caret_blink = true
 	input.caret_blink_interval = 0.5
-	input.custom_minimum_size = Vector2(0, 68)
+	input.custom_minimum_size = Vector2(0, 56)
 	input.add_theme_font_size_override("font_size", 17)
 	input.add_theme_font_override("font", Brand.font)
 	parent.add_child(input)
@@ -487,6 +487,9 @@ func _update_responsive_layout() -> void:
 	var layout_width := size.x
 	if layout_width <= 0.0:
 		layout_width = get_viewport_rect().size.x
+	var layout_height := size.y
+	if layout_height <= 0.0:
+		layout_height = get_viewport_rect().size.y
 	var compact_desktop := layout_width < 900.0
 	var mobile_web := false
 	if OS.has_feature("web"):
@@ -505,7 +508,16 @@ func _update_responsive_layout() -> void:
 		theme_button.custom_minimum_size = Vector2(44, 44)
 		theme_button.position = Vector2(-58, 14)
 		theme_button.add_theme_font_size_override("font_size", 20)
-		auth_panel.custom_minimum_size = Vector2(640, 790) if compact_desktop else Vector2(710, 820)
+		# 1000/1010 comfortably fits every view (login/register/reset/steam)
+		# without the inner ScrollContainer kicking in, on any window tall
+		# enough to hold it - but clamp to whatever height is actually
+		# available so a short window shrinks the panel (and lets the
+		# ScrollContainer take over) instead of the panel overflowing off
+		# the top/bottom of the screen.
+		var available_panel_height := layout_height - 56.0
+		var target_height := 1010.0 if compact_desktop else 1000.0
+		var panel_height := clampf(available_panel_height, 400.0, target_height)
+		auth_panel.custom_minimum_size = Vector2(640 if compact_desktop else 710, panel_height)
 		panel_gutter.add_theme_constant_override("margin_right", 28)
 		_apply_compact_scale(panel_content, 1.0)
 	_apply_theme()