Rename Fetch to Generate for recommended reviewers

What does this MR do and why?

Renames the Fetch button in the Recommended row of the reviewers sidebar to Generate. The button starts the Recommend Reviewers flow (recommend_reviewers/v1), which creates new recommendations. It does not retrieve existing ones, so Generate describes the action better.

Changes:

• Button text SuggestedReviewers|Fetch → SuggestedReviewers|Generate, and aria-label Fetch recommended reviewers → Generate recommended reviewers.
• locale/gitlab.pot regenerated with tooling/bin/gettext_extractor.
• Jest assertions and it/describe wording that names the button label are updated.
• Docs: the steps under Request recommendations for an existing merge request now say Generate. The heading is unchanged, so existing anchors still work.

Internal identifiers stay the same: fetchRecommendations, showFetchPrompt, fetchRequested, isFetching, the findFetch* spec helpers, and the fetch-recommendations and fetch-recommendations-prompt data-testids. Renaming them would be an unrelated refactor, and the testids could be referenced by E2E tests. No other doc/, qa/, spec/, or ee/ references to this button were found.

There is no new history entry. The Fetch button was added in !260988 (merged), which merged in 19.5. This rename targets the same milestone. The commit includes a Changelog: changed trailer in case this MR misses the 19.5 cutoff.

References

• Follow-up to !260988 (merged)

Screenshots or screen recordings

The only visible change is the button label: Fetch becomes Generate.

Before	After

How to set up and validate locally

1. In GDK, use a top-level group with GitLab Duo Agent Platform available.
2. For the top-level group, turn on Allow flow execution, Allow foundational flows, and the Recommend Reviewers flow.
3. Open a merge request that was created before you turned on the flow.
4. In the right sidebar, under Reviewers, confirm the Recommended row shows an enabled Generate button.
5. Select Generate and confirm the button shows a loading state while the flow runs.

MR acceptance checklist

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