Free tier raised from 100 to 500 renders a month

The free plan now includes 500 renders a month, no card and no confirmation email. Every public page saying 100 was updated in the same change.

The free plan is now 500 renders a month, up from 100. No card, no confirmation email, and the limit is a hard stop rather than an overage invoice.

100 was not enough to evaluate the API on a real project. Twelve public mentions of the old number were updated in the same commit, and the billing tests now read the plan definition rather than a literal, so a future change cannot leave the docs and the code disagreeing.