[No QA] Docs updates for E/A#95217 document marking a chat or message as unread

[MelvinBot]

Explanation of Change

Help site follow-up for Show New message marker when a user marks their own message as unread (Expensify/App#95217), which $ The green "New" marker is not shown when marking your own message as unread (Expensify/App#94794).

That PR changed user-visible behavior: marking your own message as unread now anchors the green New marker above it, the marker stays put while you remain in the chat, and a message you just sent still never gets the marker. It also added manuallyMarkedUnreadReportActionID so the marker anchors to the marked message by ID and relocates if that message is deleted.

Mark as unread, Mark as read, and the New marker had no coverage anywhere on the help site — grep -ril "mark as unread" docs/articles/ returned nothing. So rather than correcting a stale article, this adds the missing one.

What this PR does:

• Adds docs/articles/new-expensify/chat/Mark-a-Chat-or-Message-as-Unread.md, covering how to mark an individual message as unread, how to mark a whole chat as unread or read, what the New marker shows, and how long it stays.
• Registers the article under the Chat hub in docs/_data/_routes.yml.

Why a new article instead of extending Chat-Features-and-Moderation-Tools.md: docs/HELP_AUTHORING_GUIDELINES.md Section 1 requires one primary workflow per article and says to split when multiple are detected. That article already covers sending, formatting, editing, deleting, reporting, and membership, so adding a sixth workflow would compound the existing violation.

UI labels verified against source (I could not verify them against the running app — see the note below), so every label in the article is the exact product string:

Article text	Source
Mark as unread	src/languages/en.ts:874
Mark as read	src/languages/en.ts:875
New (marker text)	src/languages/en.ts:84, rendered by src/components/UnreadActionIndicator.tsx:30

Behavioral claims are sourced the same way:

• Mark as unread shows on a message and on a chat that is currently read — ContextMenuActions.tsx:544-546.
• Mark as read shows only on a chat, and only when it is unread, which is why the article says it is not available on an individual message — ContextMenuActions.tsx:624.
• Opening a chat marks it read, which is the basis for "Opening the chat again marks it as read and clears the marker" — useMarkAsRead.ts:178.

./.github/scripts/createDocsRoutes.sh (the check validateDocsRoutes.yml runs) passes.

Important

I could not verify this against the running app. I asked a web tester to walk the flow, but the message context menu could not be opened in the headless session: right-click returned UNSUPPORTED_OPERATION, long-press is unsupported on web, and hover was accepted but never triggered the app's hover state. Everything above is read from source, not observed. The claim most worth a human check is how long the marker survives: PR Expensify/App#95217's own test steps say the marker is still shown after navigating away and back, but the merged code clears manuallyMarkedUnreadReportActionID on the return trip and on refresh, and opening the chat marks it read. I wrote the article to match the merged code. If the marker really does persist across a return trip, the "How long the New marker stays on a message" section needs to change.

Fixed Issues

$
PROPOSAL:

Tests

// TODO: The human co-author must fill out the tests you ran before marking this PR as "ready for review"

• Verify that no errors appear in the JS console

Offline tests

N/A — documentation-only change. No app code is touched.

QA Steps

// TODO: The human co-author must fill out the QA tests you ran before marking this PR as "ready for review".

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I followed the guidelines as stated in the Review Guidelines
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• If a new CSS style is added I verified that:
  • A similar style doesn't already exist
  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG))
• If new assets were added or existing ones were modified, I verified that:
  • The assets are optimized and compressed (for SVG files, run npm run compress-svg)
  • The assets load correctly across all supported platforms.
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• If the PR modifies a component related to any of the existing Storybook stories, I tested and verified all stories for that component are still working as expected.
• If the PR modifies a component or page that can be accessed by a direct deeplink, I verified that the code functions as expected when the deeplink is used - from a logged in and logged out account.
• If the PR modifies the UI (e.g. new buttons, new UI components, changing the padding/spacing/sizing, moving components, etc) or modifies the form input styles:
  • I verified that all the inputs inside a form are aligned with each other.
  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• I added unit tests for any new feature or bug fix in this PR to help automatically prevent regressions in this user flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

N/A — documentation-only change. The article includes two <!-- SCREENSHOT: --> placeholders per docs/HELP_AUTHORING_GUIDELINES.md Section 8, for the context menu showing Mark as unread and for the New marker in a chat.

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@Ollyws, please review the files changed and confirm they reflect the current behavior. Then post a new comment saying @MelvinBot mark this PR as ready for review.

[OSBotify]

A preview of your ExpensifyHelp changes have been deployed to https://5c2a825d.helpdot.pages.dev ⚡️

Updated articles:

• articles/new-expensify/chat/Mark-a-Chat-or-Message-as-Unread