docs: PPR cleanup in creator facing docs

[Priban]

Summary

• Remove all PPR (pay-per-result) references from creator-facing docs
• Delete the pay_per_result.mdx page and orphaned PPR images
• Update monetization comparison table and pricing model lists to PPE + Rental only
• Fix broken links (missing hrefs, absolute → relative URLs)

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Note

Low Risk
Low risk documentation-only changes that remove the deprecated PPR pricing model from creator-facing guides and adjust links/tables accordingly; main risk is broken or missed cross-references in docs navigation.

Overview
Removes creator-facing documentation for the deprecated pay-per-result (PPR) model, including deleting the pay_per_result.mdx page and stripping PPR sections/examples from monetization guidance.

Updates monetization docs to present only pay-per-event (PPE) and rental, including revised comparison tables, pricing model lists, and related wording (e.g., pricing_and_costs.mdx, pay_per_event.mdx, publishing pages). Also fixes/normalizes several internal links and adds the RentalSunset notice to the monetization index.

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