Add live RZ Points balance widget to question and shell headers

Wires the recently-merged question-completion-credits backend
(GET /api/credits) into the client for the first time: a new
CreditsService autoload fetches/caches the balance, and the embedded
credits field on first-answer responses updates it instantly with no
extra round trip. A shared CreditsBadge widget (star icon, balance,
decorative chevron per mockup) surfaces it in both the question
screen toolbar and the main shell header.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

scripts/ui/main.gd

@@ -3,6 +3,7 @@ extends Control
 const Style := preload("res://scripts/ui/ui_style.gd")
 const Brand := preload("res://scripts/ui/medmind_style.gd")
 const NavigationRoutes := preload("res://scripts/ui/navigation_routes.gd")
+const CreditsBadge := preload("res://scripts/ui/credits_badge.gd")
 
 var screens := {}
 var _account_profile_synced := false
@@ -29,6 +30,7 @@ var drawer_open := false
 var menu_button: Button
 var account_button: Button
 var account_chevron_button: Button
+var credits_badge: PanelContainer
 var account_menu: PanelContainer
 var nav_buttons: Dictionary = {}
 var current_nav_key := "home"
@@ -204,6 +206,9 @@ func _build_ui() -> void:
 	_style_account_chevron(account_chevron_button)
 	header.add_child(account_chevron_button)
 
+	credits_badge = CreditsBadge.new()
+	header.add_child(credits_badge)
+
 	var screens_container := MarginContainer.new()
 	screens_margin = screens_container
 	screens_host = screens_container
@@ -769,6 +774,7 @@ func _on_auth_changed() -> void:
 		if not _account_profile_synced:
 			_account_profile_synced = true
 			AccountProfileService.refresh()
+			CreditsService.refresh()
 	else:
 		_account_profile_synced = false
 	if AuthState.is_logged_in and AuthState.requires_legal_acceptance and current_screen_name not in ["login", "legal_consent"]:
@@ -797,6 +803,8 @@ func _on_theme_changed(is_dark_mode: bool) -> void:
 		_style_account_avatar(account_button)
 	if account_chevron_button != null:
 		_style_account_chevron(account_chevron_button)
+	if credits_badge != null:
+		credits_badge.refresh_theme_controls()
 	if sidebar != null:
 		sidebar.add_theme_stylebox_override("panel", _sidebar_box())
 	if header_panel != null: