feat(landing): Add ComingSoon component for undocumented API sections

[kss2002]

Summary

Add a reusable ComingSoon component to display a placeholder message for component API sections that are still under development.

Changes

• New: apps/landing/src/components/ComingSoon.tsx - Reusable placeholder component with styled UI
• Updated: 19 empty Api.mdx files now display the Coming Soon placeholder instead of blank content

Affected Components

textarea, uploader, dropdown, pagination, footer, tooltip, snackbar, progress-bar, confirm, label, slider, tab, search, date-picker, menu, bottom-sheet, color-picker, header, theme-button

Why

Previously, visiting undocumented component pages showed empty content under the "Examples" section, which could confuse users. This change provides clear feedback that the documentation is coming soon.

Screenshot

Before	After

How to Test

1. Run bun run --filter landing dev
2. Navigate to /components/textarea
3. Verify the "Coming Soon" message is displayed

Notes

To add documentation for a component later, simply replace <ComingSoon /> with the <PropsTable /> component in the corresponding Api.mdx file.

Issues

feat #559

[owjs3901]

resolved #555

[codecov]

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