[NO-JIRA][BpkCardList] Remove initiallyInViewCardIndex prop

[Jimmy cook (jimmycook)]

Summary

• Removes initiallyInViewCardIndex from BpkCardList and the row/rail container, plus the supporting initialPageIndex plumbing through BpkCardListCarousel and usePageScrollSync.
• Drops the dedicated story, tests, and prop-passes; tests still pass (60/60 in bpk-component-card-list).

Why

The prop ran scrollIntoView from a mount-time useEffect. When the carousel mounts inside a parent that hasn't laid out yet (e.g. AnimateHeight at display: none), the target card has a zero-size box and the scroll silently no-ops, leaving DOM and React state out of sync.

Its sole intended consumer — ExpandedPricingOption in web-platform — hit exactly this and has since switched to a manual ref-based scroll triggered after its AnimateHeight animation completes (IRN-6568, web-platform commit 29b3db2687). Codebase search shows no other consumers, so the prop is dead weight with a misleading API.

Drafted as part of an internal decision doc: ~/.claude/tmp/remove-bpkcardlist-initial-selection.md.

Test plan

• npx jest packages/backpack-web/src/bpk-component-card-list — 60/60 passing
• tsc --noEmit clean for packages/backpack-web
• Storybook smoke check on RowToRail / RowToStack examples
• Confirm with consuming teams (none expected) that no app references the prop

🤖 Generated with Claude Code

[skyscanner-backpack-bot]

Visit https://backpack.github.io/storybook-prs/4553 to see this build running in a browser.

[skyscanner-backpack-bot]

	Warnings
⚠️	Package source files (e.g. packages/package-name/src/Component.js) were updated, but snapshots weren't. Have you checked that the tests still pass?

Browser support

If this is a visual change, make sure you've tested it in multiple browsers.

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