Social: render JetpackFooter on all sites for parity with peer pages

[CGastrell]

Proposed changes

SocialAdminPage passes showFooter={ isJetpackSite } to <AdminPage>, where isJetpackSite = isJetpackSelfHostedSite(). On WordPress.com (Simple and Atomic), this resolves to false, hiding the <JetpackFooter>.

Every other Jetpack admin page — Newsletter, Search, Backup, Protect, VideoPress, Boost, Jetpack Network Admin — renders the footer unconditionally (the default). Social was the lone exception, creating a visible inconsistency on WordPress.com. This PR drops the override so showFooter falls back to its true default.

The isJetpackSite variable is still used two lines up for the "Use license key" action button and for gating the pricing page, so it stays; only the showFooter prop is removed.

Introduced in #41393 (2023). The original rationale (hiding "irrelevant UI" on WordPress.com) no longer holds now that the footer is standard chrome across all Jetpack admin surfaces.

Related product discussion/links

• Follow-up to Admin pages: unify layout under jetpack-admin-page-layout mixin #48109 (admin-page layout unification) and Admin pages: honor WP.com nav-unification 272px sidebar width #48182 (nav-unification sidebar fix), both of which treat the JetpackFooter as a pinned, always-present element.

Does this pull request change what data or activity we track or use?

No.

Testing instructions

1. On a WordPress.com site (Simple or Atomic), open /wp-admin/admin.php?page=jetpack-social.
2. Verify the Jetpack footer ("An Automattic Airline" + Jetpack logo) is now rendered, pinned at the bottom of the content column.
3. Compare against admin.php?page=jetpack-newsletter and admin.php?page=jetpack-search — all three should now present the same footer treatment.
4. On a self-hosted Jetpack site, verify nothing regresses — the footer was already rendering there, and should continue to.
5. Verify the "Use license key" button still appears on self-hosted sites without paid Social features (the isJetpackSite check for that button is unchanged).

🤖 Generated with Claude Code

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the fix/social-admin-page-restore-footer branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack fix/social-admin-page-restore-footer

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

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Follow this PR Review Process:

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Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

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