[No QA] Docs updates for E/A#86864 Merchant Rule behavior when applied tag is deleted

[MelvinBot]

Explanation of Change

Help site follow-up for #86864, which changed how a Merchant Rule behaves when the tag it applies is deleted from the workspace. After that PR, the rule keeps its stored tag value but the deleted tag is no longer shown in the rule summary or the rule edit page, and matching expenses no longer get a system message with an empty tag. That PR also filters the tag options in a rule so only tags valid under the already-selected parent levels are listed.

docs/articles/new-expensify/workspaces/Workspace-Merchant-Rules.md:

• Added a behavior bullet under How Merchant Rules are applied: deleting a tag stops that one update, while the rule's other updates still apply.
• Added the deleted tag to the list of reasons in Why didn't my Merchant Rule apply?.
• Added the FAQ What happens to a Merchant Rule when the tag it applies is deleted?, covering what admins see in the rule summary and the rule's Tag field, and how to set a tag again.
• Added the FAQ Why don't all of my tags appear when I select Tag in a Merchant Rule?, covering disabled tags and multi-level tag filtering.
• Corrected the save step to the exact UI label, Save rule (the article had "Save Rule").
• Added keywords for the deleted tag searches.

Written against docs/HELPSITE_NAMING_CONVENTIONS.md, docs/HELP_AUTHORING_GUIDELINES.md, and docs/TEMPLATE.md: one workflow per article, task-based ## headings, no new # headings, bolded UI labels in Sentence case, and a relative cross-link.

UI labels (Merchant section, Add merchant rule, Save rule, Tag) were checked against the strings in src/languages/en.ts. The live UI check could not be completed in this run because the test session never rendered the app, so please confirm the labels when you review.

Fixed Issues

$ #82690
PROPOSAL:

Docs follow-up for #86864.

Tests

// TODO: The human co-author must fill this out before marking this PR as "ready for review". This PR changes help site markdown only, with no product code changes.

• Verify that no errors appear in the JS console

Offline tests

N/A - help site markdown only.

QA Steps

// TODO: These must be filled out, or the issue title must include "[No QA]."
// The human co-author must fill out the QA steps 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

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

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@truph01, 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://31a364a0.helpdot.pages.dev ⚡️

Updated articles:

• articles/new-expensify/workspaces/Workspace-Merchant-Rules