Ko-fi Support

[BittuBarnwal7479]

Clear and concise description of the problem

I'd like SponsorKit to support Ko-fi so tips and memberships can be included in generated sponsor images.

I'm working on a PR for this.

Suggested solution

Add a kofi provider that receives Ko-fi webhooks, verifies the token, stores payments locally, and converts public tips and subscriptions into SponsorKit sponsorships.

The provider should also deduplicate webhook retries and avoid storing private supporter information.

Alternative

Users could write a custom provider and manually import Ko-fi payment data, but that would not support automatic updates.

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guide.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.