Use PrimeVue Avatar component

[huchenlei]

This PR introduces several improvements to the user interface components:

1. Avatar Component Standardization:

   • Replaced custom avatar implementations with PrimeVue's Avatar component
   • Applied consistent styling and behavior across user-related components
   • Improved accessibility with proper aria-label attributes

2. CurrentUserButton Improvements:

   • Simplified the button structure and styling
   • Replaced manual avatar/icon handling with PrimeVue's Avatar component
   • Improved computed property for photoURL with proper type safety
   • Added padding to the chevron icon for better spacing

3. UserPanel Refinements:

   • Updated avatar display to use PrimeVue's Avatar component
   • Improved layout and spacing in the user information section
   • Maintained consistent styling with the rest of the application

The changes focus on standardizing the user interface components, improving code maintainability, and enhancing the visual consistency of the application.

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