fix: correct default title behavior in alert component when only color is provided

[zihanKuang]

Problem

The alert shortcode currently uses the type parameter to determine the styling and default title (e.g., "Danger", "Warning", "Info", "Note"). However, many usages of the alert shortcode in the documentation only specify the color parameter without setting the type parameter.

Cause

• The current implementation does not dynamically adjust the title based on the color parameter.
• It assumes that either type is provided, or if not, defaults to "Success" without checking the color.

Solution

In the fallback branch (when no recognized type is provided), I added logic to dynamically set a default title based on the color parameter if no explicit title is provided. The updated logic behaves as follows:

• Yes, I signed my commits.

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