feat: add missing markdown container

[chencu5958]

Description

Add ::: note, ::: important, and ::: caution container support to VitePress markdown.

These containers were defined in ContainerOptions interface but were never registered in containerPlugin, so users couldn't use them via the ::: syntax.

Changes:

• Add note container: options?.noteLabel || 'NOTE'
• Add important container: options?.importantLabel || 'IMPORTANT'
• Add caution container: options?.cautionLabel || 'CAUTION'

Usage:

::: note
This is a note.
:::

::: important
This is an important note.
:::

::: caution
This is a caution note
:::

Linked Issues

Additional Context

• All existing tests pass (34 passed, 1 skipped)
• ContainerOptions already defined noteLabel, importantLabel, cautionLabel but they were not being used
• CSS variables and styles for these containers already exist in the theme