[Feature Request] Stripe Checkout: Enable automatic invoice generation

[wangbooth]

Routine Checks

• I have confirmed there are no similar issues currently
• I have confirmed I have upgraded to the latest version
• I have thoroughly read the project README and confirmed the current version cannot meet my needs
• I understand and am willing to follow up on this issue, assist with testing and provide feedback
• I understand and acknowledge the above, and understand that project maintainers have limited time and energy, issues that do not follow the rules may be ignored or closed directly

Feature Description

When a user completes a Stripe payment, no invoice is generated. This means users cannot obtain a Stripe-issued receipt/invoice for their purchase.

Use Case

In controller/topup_stripe.go, the genStripeLink function creates a Checkout Session without enabling invoice creation:

params := &stripe.CheckoutSessionParams{
    // ...
    Mode: stripe.String(string(stripe.CheckoutSessionModePayment)),
    // InvoiceCreation is not set
}

**Suggested Fix**

Add InvoiceCreation to the Checkout Session params:

InvoiceCreation: &stripe.CheckoutSessionInvoiceCreationParams{
    Enabled: stripe.Bool(true),
},