refactor: replace internal isFullBleed usage with padding={0}

[cixzhang]

Summary

Two-part refactor that migrates away from isFullBleed on Layout components and then removes it from their interfaces entirely.

Part 1: Replace internal usages with padding={0}

Replace all internal usages of isFullBleed prop on Layout components with the equivalent padding={0}. The padding prop is more expressive (supports any spacing step, not just 0/default) and aligns with the rest of the design system API.

Files changed:

• packages/core/src/AppShell/XDSAppShell.tsx — 4 usages replaced
• apps/storybook/stories/Layout.stories.tsx — Playground story args/controls migrated
• apps/storybook/stories/Card.stories.tsx — FullBleed story migrated, deprecation note added
• apps/storybook/stories/Section.stories.tsx — FullBleed story migrated, deprecation note added

Part 2: Remove isFullBleed from Layout component interfaces

Remove the deprecated isFullBleed prop from all Layout component interfaces. Consumers must use padding={0} instead.

Files changed:

• packages/core/src/Layout/XDSLayout.tsx — removed from props interface
• packages/core/src/Layout/XDSLayoutContent.tsx — removed from props interface and implementation
• packages/core/src/Layout/XDSLayoutFooter.tsx — removed from props interface and implementation
• packages/core/src/Layout/XDSLayoutHeader.tsx — removed from props interface and implementation
• packages/core/src/Layout/XDSLayoutPanel.tsx — removed from props interface and implementation
• apps/storybook/stories/Layout.stories.tsx — removed isFullBleed argType

Also fixed

• apps/sandbox/src/app/pages/mega-menu/page.tsx — fixed pre-existing TypeScript error (inline styles position type)

What is NOT changed

• XDSCard and XDSSection — isFullBleed prop remains (maps to padding={0} internally). Follow-up removal.
• XDSDivider — its isFullBleed is a different concept (negative-margin escape hatch)
• Codemods (packages/cli/) — migrate-isFullBleed-to-padding codemod preserved for consumer migration

[github-actions]

PR Analysis Report

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Modified Components

AppShell · View in Storybook

Metric	Before	After	Delta
Bundle Size (ESM)	N/A	625B	N/A
Lines of Code	N/A	383	-
Complexity	N/A	Very High (47)	-

Layout · View in Storybook

Metric	Before	After	Delta
Bundle Size (ESM)	N/A	1.0KB	N/A
Lines of Code	N/A	899	-
Complexity	N/A	Very High (66)	-

Bundle Size Summary

Package	Size (ESM)	Size (CJS)	Gzipped
@xds/core	9.3KB	15.0KB	2.3KB

Accessibility Audit

Status: 1 accessibility violation(s) found — 1 serious.

XDSLayout - 1 issue(s)

• 🟠 serious: Ensure the contrast between foreground and background colors meets WCAG 2 AA minimum contrast ratio thresholds
  • Rule: color-contrast · Affects 3/10 stories · Learn more
  • WCAG: 1.4.3 (Level AA)

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[cixzhang]

We can clean this up