vueforge-layouts v1.21.0

Changed

• Refined the default VfAdminShell palette into a clear elevation hierarchy: a contrast topbar, recessed sidebar canvas, and elevated workspace surface in both color modes.
• Kept surface-based workspace content visually structured while preserving the public header, sidebar, and workspace background tokens for application overrides.
• Made generated layout theme CSS omit empty mode blocks when a custom preset has no mode-specific overrides.

Docs

• Updated the VfAdminShell feature and theming documentation to describe the new semantic surface hierarchy.
• Replaced the card grid in the responsive VfAdminShell showcase with a paginated warehouse data table for realistic visual verification.