Localised prices for the pricing page

Asks Paddle what a visitor in this country would pay, and returns Paddle's own formatted strings. Called by the browser instead of loading Paddle.js, so that a pricing-page visit does not disclose the visitor's IP address to a payment provider before they have asked to buy anything. The country is resolved from an offline database inside the handler and the address is not stored. Responses are cached per country, never per visitor. When Paddle cannot be reached the response carries unavailable=true and the page falls back to its EUR figures.