Replace emojis with a proper icon library

[blinkagent]

Summary

The Mux UI currently uses emojis in various places, which has been noted as contributing to a "vibe coded" feel. We should replace these emojis with icons from a proper icon library for a more polished, professional appearance.

Motivation

Using a consistent icon library instead of emojis will:

• Provide a more cohesive visual design
• Ensure consistent rendering across different platforms/browsers
• Give us more control over icon styling (size, color, etc.)
• Improve the overall professional feel of the UI

Suggested approach

1. Audit current emoji usage throughout the codebase
2. Select an appropriate icon library (e.g., Lucide, Heroicons, Phosphor)
3. Create a mapping from emojis to equivalent icons
4. Replace emojis with icon components

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Created on behalf of @mattvollmer

[mattvollmer]