feat: implement user profiles and settings

Add comprehensive user profile system allowing users to showcase
their activity and customize their profiles.

Database Changes:
- Added profile fields to User model: slug, displayName, bio, profilePublic
- Added index on slug field for efficient lookups

API Changes:
- Added GET /users/me endpoint to fetch current user
- Added PUT /users/me endpoint to update user settings
- Added GET /users/profile/:identifier endpoint for public profiles
- Updated UserService with profile methods and statistics
- Modified AuthService to include profile fields in user responses

Frontend Changes:
- Created ProfileComponent to display user profiles with stats
- Created SettingsComponent for profile customization
- Added profile and settings routes
- Updated header dropdown menu with profile links
- Enhanced UserService with profile methods
- Added updateUser method to AuthService

Features:
- Custom profile slugs for clean URLs
- Display names separate from usernames
- User bios (up to 500 characters)
- Public/private profile toggle
- Activity statistics (suggestions, likes, comments, acceptance rate)
- Badge display (Staff, Mod, VIP, Discord Member)
- Beautiful witch-themed styling

Closes #45

api/prisma/schema.prisma

@@ -182,6 +182,10 @@ model User {
   username      String
   email         String         @unique
   avatar        String?
+  slug          String?
+  displayName   String?
+  bio           String?
+  profilePublic Boolean        @default(true)
   isAdmin       Boolean        @default(false)
   isBanned      Boolean        @default(false)
   inDiscord     Boolean        @default(false)
@@ -194,6 +198,8 @@ model User {
   suggestions   Suggestion[]
   likes         Like[]
   refreshTokens RefreshToken[]
+
+  @@index([slug], map: "User_slug_key")
 }
 
 model Comment {