Fix Push MD release bundle and show PR URL after push

[artpi]

What changed

• include the Merge diff runtime used by Pull Request views in the Push MD toolkit manifest
• make ZIP inspection autoload LineDiffer from the built artifact and execute a smoke diff
• print the matching Pull Request admin URL after every successful preview-branch push

Why

The v0.6.9 WordPress.org artifact fatals while rendering a Pull Request because PushMDVendor\WordPress\Merge\Diff\LineDiffer is not present in the release bundle. Development and E2E installs use the monorepo source tree, which masked the missing manifest entries. Returning the Pull Request URL also lets the person pushing open the review directly from the terminal.

Validation

• bash bin/build-plugins.sh
• bash bin/inspect-push-md-zip.sh
• vendor/bin/phpunit plugins/push-md/Tests/ (31 tests, 36 assertions, 12 skipped E2E tests)
• full Push MD E2E suite on a clean WordPress install (31 tests, 700 assertions)
• full Push MD E2E suite against an install using the generated ZIP before the URL addition (31 tests, 698 assertions)
• targeted PHPCS on plugins/push-md/class-push-md-plugin.php
• bash -n bin/inspect-push-md-zip.sh
• git diff --check

composer lint still exits non-zero on existing repository warnings; changed production PHP passes targeted PHPCS.