A4A Marketplace: add Pressable post-checkout confirmation banner

[tiagonoronha]

Part of A4A-2724

Proposed Changes

• client/a8c-for-agencies/sections/purchases/licenses/licenses-overview/pressable-purchase-confirmation-message.tsx (new) — a success banner shown at the top of the Licenses page after a Pressable plan is purchased. It congratulates the agency, explains the next step is adding or migrating a site, and offers an Explore your Pressable dashboard button linking to the Pressable agency dashboard. It reads a pressable_purchased query arg, fires a calypso_a4a_pressable_plan_purchased Tracks event on display (and …_explore_dashboard_click on the CTA), then strips the arg from the URL.
• client/a8c-for-agencies/sections/marketplace/billing-dragon-checkout/index.tsx — when the Billing Dragon checkout contains a Pressable plan (from either the cart items or the planSlug route), the post-checkout redirect to /purchases/licenses now carries pressable_purchased=<slug> so the banner above can surface. Non-Pressable purchases redirect exactly as before.
• client/a8c-for-agencies/sections/purchases/licenses/licenses-overview/index.tsx — mounts the banner in the page’s LayoutTop, above the existing notices.

Why are these changes being made?

After buying a Pressable plan, agencies landed on the Licenses page with no guidance on what to do next. This adds a clear post-purchase confirmation that points them to their next step — adding or migrating a site — and gives them a direct way into the Pressable dashboard, so the moment after checkout is a hand-off rather than a dead end.

Testing Instructions

1. Open the live link and go to A4A → Marketplace → Hosting → Pressable.
2. Select a Pressable plan and complete checkout.
3. On returning to A4A → Purchases → Licenses, confirm a success banner appears at the top: title “Congratulations! Your Pressable plan is ready!”, the next-step copy, and an Explore your Pressable dashboard button that opens https://my.pressable.com/agency/auth in a new tab.
4. Confirm the pressable_purchased query arg is removed from the URL after the banner renders, and that reloading the page does not re-show the banner.
5. Confirm a non-Pressable purchase still returns to the Licenses page with no Pressable banner.
6. Verify there are no TypeScript / React console errors.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• For UI changes, have you tested the affected components in dark mode?
• Have you tested accessibility for your changes? Ensure the feature remains usable with various user agents (e.g., browsers), interfaces (e.g., keyboard navigation), and assistive technologies (e.g., screen readers) (PCYsg-S3g-p2).
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-183325

Jetpack Cloud Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-183325&env=jetpack

Automattic for Agencies Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-183325&env=a8c-for-agencies

Dashboard Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-183325&env=dashboard

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug add/a4a-2724-pressable-post-checkout-notice on your sandbox.

[github-actions]

Looks like one of the E2E tests has failed.

You can fix them following these steps:

1. Check out this branch locally:

   gh pr checkout 111634

2. Start Claude Code in the repo:

   claude

3. Run the /fix-e2e-tests skill, passing this PR number:

   /fix-e2e-tests 111634