Add PCI payment page script gates

[malb200710-dev]

Summary

• Adds a PCI DSS v4.0 payment page script evidence gate for Requirements 6.4.3 and 11.6.1.
• Covers hosted fields, iframes, redirects, checkout SPAs, tag managers, script inventory, authorization, integrity controls, and rendered-page tamper detection.
• Adds output reporting and a common pitfall for assuming outsourced payment processing removes checkout-page obligations.

Validation

• Local marker check passed for version 1.0.1, Req 6.4.3 / 11.6.1 gate, script inventory, output fields, and changelog.
• Fenced code block count is even.

Closes #2291

Bounty consideration requested if this review gap is accepted.