fix(stories): resolve React warnings for keys and DOM prop forwarding

[tamas-sage]

Proposed behaviour

Stories render without those warnings by adding stable keys, passing key directly, and using transient styled props for non-DOM attributes.

Current behaviour

Storybook stories show React warnings due to missing list keys, key being spread into JSX, and style-only props leaking to DOM.

Checklist

• Commits follow our style guide
• Related issues linked in commit messages if required
• Screenshots are included in the PR if useful
• All themes are supported if required
• Unit tests added or updated if required
• Playwright automation tests added or updated if required
• Storybook added or updated if required
• Translations added or updated (including creating or amending translation keys table in storybook) if required
• Typescript d.ts file added or updated if required
• Related docs have been updated if required

QA

• Tested in provided StackBlitz sandbox/Storybook
• Add new Playwright test coverage if required
• Carbon implementation matches Design System/designs
• UI Tests GitHub check reviewed if required

Additional context

Testing instructions

[Copilot]

Pull request overview

This PR removes recurring React/Storybook warnings by ensuring list-rendered elements have stable key props, avoiding spreading key into JSX props, and preventing style-only props from being forwarded to DOM elements via styled-components transient props.

Changes:

• Added stable React key props to several mapped/array-rendered Storybook examples (Tile, Portrait, Menu, FileInput).
• Updated Form footer styling to use a transient styled-components prop ($disableStickyOnSmallScreen) so it won’t leak as an invalid DOM attribute.
• Mirrored the Portrait story fix in the corresponding skills/ documentation snippet.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/components/tile/tile-test.stories.tsx	Moves key to the TileContent elements (not in spread props) and stabilizes keys in the rendered content array.
src/components/portrait/portrait.stories.tsx	Adds key to Option elements rendered from availableVariants.
src/components/menu/menu-test.stories.tsx	Adds a stable key to Menu instances rendered in a map.
src/components/form/form.style.ts	Renames a style-only prop to a transient $... prop to prevent DOM prop forwarding warnings.
src/components/form/form.component.tsx	Passes the renamed transient prop through to StyledFormFooter.
src/components/file-input/file-input-test.stories.tsx	Adds stable keys for the FileInput list in the status mapping story.
skills/carbon-react/components/portrait.md	Updates the documented Portrait story snippet to include a key on mapped Option elements.

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[edleeks87]

The fix commits will trigger a release, they should be either a chore, docs or refactor as there's no functional changes to the component

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.

[DipperTheDan]

Nothing more to add from me on this. @edleeks87 has made a valid point in his comment and I agree with him on that so it will need addressing.