Tebex/Crafting Store Integration

[Lupancham]

Allow official hosted checkout pages from Tebex or CraftingStore to be opened directly inside the client via an embedded webview/iframe, instead of requiring an external browser.

• Must ensure no proxying or modification of checkout traffic.
• Must confirm embedding is permitted under Tebex/CraftingStore ToS.
• Must preserve all security headers (CSP, X-Frame-Options).
• Must ensure no card/payment data is handled by the client or server (PCI remains with the payment processor).
• Confirm provider policy on embedding.
• Confirm client webview does not strip security headers.