[ZEPPELIN-6661] Cover notebook editor save timing

[voidmatcha]

What is this PR for?

When a paragraph save response arrives late, ParagraphBase treats it as a remote update and replaces the editor text, losing edits typed in the meantime.

This PR tracks pending saves by msgId. A response to one of the user's own saves no longer replaces the editor text when a newer edit or save followed it; otherwise the response is the server copy and is applied as before. Other paragraph fields in that response always apply.

Related behavior changes in ParagraphBase:

• A remote edit that differs from the local unsaved text now replaces it and resets the saved baseline, so the discarded local text is not re-committed later.
• An empty local edit (all text deleted) is now treated as a local edit and protected like any other.
• A broadcast that does not match a pending local save and repeats the saved text no longer rewinds the editor while the user is typing.

This PR adds the E2E scenarios for ZEPPELIN-6661 (idle autosave, edit during an in-flight save). The in-flight scenario fails without this fix, so the fix is included here.

What type of PR is it?

Bug Fix

Todos

• Match save responses to pending saves by msgId
• Add unit tests and browser scenarios for save timing
• Register the scenarios in the notebook parity inventory

What is the Jira issue?

ZEPPELIN-6661

How should this be tested?

cd zeppelin-web-angular
npx vitest run --config vitest.shell.config.mts src/app/core/paragraph-base/paragraph-base.spec.ts
npm run check:notebook-parity-scenarios
CI=true PLAYWRIGHT_HTML_OPEN=never npm run e2e -- --reporter=list tests/notebook/persistence/notebook-save-timing.spec.ts

Screenshots (if appropriate)

N/A

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No

[voidmatcha]

This is why the PR changes Angular code. On master, an edit typed while a save is in flight is overwritten when the delayed save response arrives. This branch puts only this PR's E2E files on master, without the fix: https://github.com/voidmatcha/zeppelin/tree/ZEPPELIN-6661-repro-on-master

CI results (Playwright, anonymous mode):

App code	NB-PARITY-050	NB-PARITY-051
master (run)	pass	fails on Chromium, Firefox and WebKit: the editor rewinds to %md First pending save (expected %md First pending save; latest edit wins)
this PR	pass	pass

Angular changes:

• ParagraphBase: tracks sent saves by msgId; a response to the user's own save no longer changes the editor text.
• NotebookParagraphComponent: records the msgId when it commits a paragraph.
• MessageService: passes the msgId of PARAGRAPH responses to the handler.
• SDK Message.send() and commitParagraph(): return the sent msgId.