Add Stripe donation flow

scripts/ui/main.gd

@@ -314,6 +314,11 @@ func _build_ui() -> void:
 	bookmarks.main = self
 	screens_container.add_child(bookmarks)
 	screens["bookmarks"] = bookmarks
+	var donations := preload("res://scripts/ui/donation_screen.gd").new()
+	donations.name = "DonationScreen"
+	donations.main = self
+	screens_container.add_child(donations)
+	screens["donations"] = donations
 
 	feedback_dialog = preload("res://scripts/ui/app_feedback_dialog.gd").new()
 	feedback_dialog.name = "AppFeedbackDialog"
@@ -386,6 +391,7 @@ func _populate_navigation(container: VBoxContainer, include_brand: bool) -> void
 	spacer.size_flags_vertical = Control.SIZE_EXPAND_FILL
 	container.add_child(spacer)
 	container.add_child(HSeparator.new())
+	_add_nav_button(container, "donations", "Support MedMind", "heart-pulse", true)
 	_add_nav_button(container, "performance", "Profile", "user-round", true)
 	_add_nav_button(container, "settings", "Settings", "settings", true)
 	_add_nav_button(container, "logout", "Log out", "log-out", true)
@@ -426,6 +432,7 @@ func _on_navigation_pressed(key: String) -> void:
 		"settings": show_screen("settings")
 		"notes": show_screen("notes")
 		"bookmarks": show_screen("bookmarks")
+		"donations": show_screen("donations")
 		"logout": _logout()
 
 
@@ -440,7 +447,8 @@ func _update_header_title(screen_name: String) -> void:
 		"profile": "Profile",
 		"settings": "Settings",
 		"notes": "Notes",
-		"bookmarks": "Bookmarks"
+		"bookmarks": "Bookmarks",
+		"donations": "Support MedMind"
 	}
 	header_title.text = str(titles.get(screen_name, ""))
 
@@ -735,6 +743,9 @@ func _on_theme_changed(is_dark_mode: bool) -> void:
 	var selector = screens.get("selection")
 	if selector != null and selector.has_method("refresh_theme_controls"):
 		selector.refresh_theme_controls()
+	var donations = screens.get("donations")
+	if donations != null and donations.has_method("refresh_theme_controls"):
+		donations.refresh_theme_controls()
 	var player = screens.get("player")
 	if player != null and player.has_method("refresh_theme_controls"):
 		player.refresh_theme_controls()