Move legacy landing pages and forms to legacy_landing_pages endpoint

[ciccio-kit]

Summary

Moves the WordPress libraries off the landing_pages API endpoint, which the monolith is about to repurpose. Both methods that hit it now call the new byte-identical legacy_landing_pages endpoint (Kit/convertkit#44872, confirmed live in production):

• get_legacy_landing_pages() — type => hosted
• get_legacy_forms() — type => embed

The new endpoint supports both type filters and returns the same shape (keyed legacy_landing_pages, same pagination object), so nothing else changes. After this, no code calls the old landing_pages endpoint.

This is shared library code (convertkit-wordpress / wpforms / membermouse) — releasing needs a new tag (next: 2.1.7) and a composer bump in each consuming plugin.

Testing

No test changes are required: the integration tests already exercise both methods and assert on the legacy_landing_pages response key — APITest::testGetLegacyLandingPages / testGetLegacyLandingPagesWithTotalCount, testGetLegacyForms / testGetLegacyFormsWithTotalCount, and ResourceTest::testRefreshLandingPages (which drives get_legacy_landing_pages() via refresh()). None hardcode the endpoint path, so the switch is transparent.

Checklist

• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• I have assigned a reviewer or two to review this PR

[n7studios]

Thanks for submitting this PR. Tests are failing due to other API changes, which I'll resolve in another PR.