Add Stripe donation flow

scripts/ui/donation_amount.gd

@@ -0,0 +1,18 @@
+extends RefCounted
+
+
+static func parse_cents(value: String) -> int:
+	var cleaned := value.strip_edges().trim_prefix("$").replace(",", "")
+	var matcher := RegEx.new()
+	matcher.compile("^[0-9]+(?:\\.[0-9]{1,2})?$")
+	if matcher.search(cleaned) == null:
+		return -1
+	var parts := cleaned.split(".")
+	var dollars := int(parts[0])
+	var cents := 0
+	if parts.size() == 2:
+		var fraction := str(parts[1])
+		cents = int(fraction) * (10 if fraction.length() == 1 else 1)
+	if dollars > 10000 or (dollars == 10000 and cents > 0):
+		return -1
+	return dollars * 100 + cents