feat: add hovercard component

[LeoDanielA01]

What does this PR do?

Introduces a new HoverCard component to Frappe UI for displaying
rich, contextual information on hover or keyboard focus.

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Why is this needed?

Current tooltips in Frappe UI are suitable only for short text.
Many ERP use cases require richer contextual previews such as:

• User / owner information
• Inline help with formatting
• Metadata previews
• Contextual explanations without opening dialogs

HoverCard fills this gap without adding modal overhead.

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Features

• Hover and keyboard focus triggers
• Accessible by default (focusable, non-blocking)
• Supports rich content
• Lightweight alternative to dialogs
• Reusable and composable API
• No breaking changes