CEXT-6402: move banner-notification/custom-mass-actions into v1/

[obarcelonap]

Description

Move the V1 banner-notification/custom-mass-actions sample into admin-ui-sdk/v1/ as part of the Admin UI SDK V1/V2 migration (CEXT-6400).

Banner notifications have no standalone V2 equivalent — in V2 they are declared inline on each mass action as notifications.success / notifications.error. This is documented in the admin-ui-sdk/README.md comparison table.

Related Issue

CEXT-6402 / CEXT-6400

Motivation and Context

Organising V1-only samples under admin-ui-sdk/v1/ to clearly separate them from future V2 samples.

How Has This Been Tested?

Sample deployed to App Builder stage (project CEXT6400, workspace CEXT6402). Registration endpoint returns the expected payload with bannerNotification.massActions.order and .product entries.

App URL: https://development-271530-cext6400-cext6402.dev.runtime.adobe.io/index.html

Screenshots (if appropriate):

N/A

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[obarcelonap]

Superseded by the approach of folding banner notification config into companion mass-action/view-button samples (CEXT-6410, CEXT-6413, CEXT-6411). Sample deletions will happen in the context of each companion ticket. README update applied to PR #53 instead.