Add /profile slash command with rich Discord embeds

[Copilot]

This PR implements a new /profile slash command that displays user profile information using rich Discord embeds, providing a modern alternative to the existing image-based !profile command.

Features

• Modern Interface: Uses Discord's slash command system for better UX
• Rich Embeds: Beautiful, organized display with user avatars and role colors
• Comprehensive Data: Shows all profile information including:
  • User info (username, display name, main role)
  • Level & XP (total, current progress, percentage, rank)
  • Karma statistics (total, weekly, monthly, given, rank)
  • Optional location display if DefaultCity is set
• Flexible Usage:
  • /profile - Shows your own profile
  • /profile @user - Shows another user's profile
• Error Handling: Graceful handling of missing user data

Example Usage

🎮 JohnDoe's Profile                    [Avatar]
────────────────────────────────────────────────

👤 User Info
Username: JohnDoe
Display Name: John Developer  
Main Role: Unity Developer

📈 Level & Experience          ⭐ Karma
Level: 25 (Rank #47)          Total Karma: 156 (Rank #23)
Total XP: 45,687              Weekly: 12
Current Level XP: 1,234/2,890 Monthly: 45
                              Karma Given: 89

Technical Implementation

• Added to UserSlashModule.cs following existing patterns
• Reuses existing database queries and user data models
• Includes proper dependency injection and error handling
• Future-ready with placeholder for achievement system (issue Achievement/Badge System #341)

Benefits

✅ Instant display (no image generation time)
✅ Accessible and copy-paste friendly
✅ Lower server resource usage
✅ Works on all Discord clients
✅ Complements existing !profile command

Fixes #342.

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[Pierre-Demessence]

/deploy_dev

[github-actions]

🚀 Starting deployment of Unity-Developer-Community/UDC-Bot:copilot/fix-342 to development...