Add Tests

Merged initial pull request to fix the Example module.
Still need to work on Functional Javascript tests.

Merged as MR !20.

ParagraphsIEFEmbedTest now covers the flow this module exists for, in a real browser:

• the CKEditor 5 toolbar button opens the dialog, and the module's own entity browser widget renders one button per allowed paragraph type;
• choosing a type loads that type's inline entity form in the iframe;
• saving it returns to the dialog, where this module has replaced the back button with one that opens the paragraph's own edit form;
• Embed inserts the widget, and the saved node renders the paragraph.

None of that is reachable from BrowserTestBase — the toolbar button, the iframe, the inline form and the embed step are all AJAX, which is why the earlier tests stopped at "the form renders".

Two things worth recording from writing them.

Editors need a permission that is easy to miss: Entity Browser generates "access <browser> entity browser pages" per browser, and without access paragraph_items entity browser pages the dialog opens on an access denied page rather than the type selector. That was the first thing the test hit. It is now documented — see #3619188.

Selecting an embedded entity logs a JavaScript error from Entity Embed, which would fail any test that embeds anything. Rather than turn the console check off, the test discards that one error by signature and still fails on any other. See #3619182.

The container ships no browser, so the Makefile grew selenium-start and test-local-js. CI needed no change: its test jobs already attach a Selenium service and run every suite in the module. Verified the tests genuinely execute there rather than being skipped — the phpunit job log shows both methods passing against Chrome 127.