[No QA] Docs updates for E/A#99527 joining an existing travel billing feed - #100749

Explanation of Change

Help site follow-up for #99527, which lets a Workspace join an existing Consolidated Travel Billing feed on the domain instead of always provisioning its own.

docs/articles/travel/consolidated-travel-billing/Enable-Consolidated-Travel-Billing-in-a-Workspace.md previously described only one path after switching the toggle on: add or select a settlement bank account. That is now the fallback path. When the admin already administers a configured travel feed, a feed list opens first, with a Set up a new travel feed option at the bottom.

Changes:

• Added the feed-selection step to How to enable Consolidated Travel Billing in a Workspace and renumbered the steps that follow.
• Added a How to join an existing Consolidated Travel Billing feed section explaining both branches, including that joining a feed reuses that feed's settlement account so no bank account is requested.
• Added two FAQ entries: sharing one feed across two Workspaces, and why no feeds appear in the list.
• Updated keywords and internalScope metadata to cover the joining workflow.
• Added a <!-- SCREENSHOT: --> suggestion for the feed list, per the authoring guidelines.

Applied docs/HELPSITE_NAMING_CONVENTIONS.md, docs/HELP_AUTHORING_GUIDELINES.md, and docs/TEMPLATE.md: one # title plus # FAQ, task-based ## headings, bolded UI labels in Sentence case, relative cross-links only.

UI label verification: Travel (workspace settings row, under Spend in More features) was confirmed live in the web app. Consolidated Travel Billing and Set up a new travel feed were confirmed against src/languages/en.ts on the head branch — the section is gated behind Expensify Travel's business-verification flow, which the test account cannot complete, so those two strings were not observed rendered. Please confirm them.

Fixed Issues

$ https://github.com/Expensify/Expensify/issues/662524
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.

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)
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• 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)
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  • A similar style doesn't already exist
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Screenshots/Videos

@allgandalf, 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.