Add project files.

BudgetApp/Services/CategoryService.cs

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+using Microsoft.EntityFrameworkCore;
+using BudgetApp.Data;
+
+namespace BudgetApp.Services;
+
+public class CategoryService
+{
+    private readonly ApplicationDbContext _db;
+
+    private static readonly (string Name, string Icon)[] DefaultCategories =
+    [
+        ("Groceries", "🛒"),
+        ("Rent / Mortgage", "🏠"),
+        ("Utilities", "💡"),
+        ("Transport", "🚗"),
+        ("Eating Out", "🍽️"),
+        ("Entertainment", "🎬"),
+        ("Health", "🏥"),
+        ("Insurance", "🛡️"),
+        ("Salary", "💰"),
+        ("Savings", "🏦"),
+        ("Subscriptions", "📱"),
+        ("Shopping", "🛍️"),
+        ("Education", "📚"),
+        ("Travel", "✈️"),
+        ("Gifts", "🎁")
+    ];
+
+    public CategoryService(ApplicationDbContext db)
+    {
+        _db = db;
+    }
+
+    public async Task<List<Category>> GetCategoriesAsync(string userId)
+    {
+        return await _db.Categories
+            .Where(c => c.UserId == userId)
+            .OrderBy(c => c.Name)
+            .ToListAsync();
+    }
+
+    public async Task EnsureDefaultCategoriesAsync(string userId)
+    {
+        var existing = await _db.Categories
+            .Where(c => c.UserId == userId)
+            .ToListAsync();
+
+        if (existing.Count == 0)
+        {
+            var defaults = DefaultCategories.Select(d => new Category
+            {
+                Name = d.Name,
+                Icon = d.Icon,
+                UserId = userId
+            });
+
+            _db.Categories.AddRange(defaults);
+            await _db.SaveChangesAsync();
+            return;
+        }
+
+        // Backfill icons on existing default categories that have empty icons
+        var defaultLookup = DefaultCategories.ToDictionary(d => d.Name, d => d.Icon);
+        bool updated = false;
+
+        foreach (var category in existing)
+        {
+            if (string.IsNullOrEmpty(category.Icon) && defaultLookup.TryGetValue(category.Name, out var icon))
+            {
+                category.Icon = icon;
+                updated = true;
+            }
+        }
+
+        if (updated)
+        {
+            await _db.SaveChangesAsync();
+        }
+    }
+
+    public async Task CreateCategoryAsync(Category category)
+    {
+        _db.Categories.Add(category);
+        await _db.SaveChangesAsync();
+    }
+
+    public async Task UpdateCategoryAsync(int id, string userId, string name, string icon)
+    {
+        var category = await _db.Categories
+            .FirstOrDefaultAsync(c => c.Id == id && c.UserId == userId);
+        if (category is not null)
+        {
+            category.Name = name;
+            category.Icon = icon;
+            await _db.SaveChangesAsync();
+        }
+    }
+
+    public async Task DeleteCategoryAsync(int id, string userId)
+    {
+        var category = await _db.Categories
+            .FirstOrDefaultAsync(c => c.Id == id && c.UserId == userId);
+        if (category is not null)
+        {
+            _db.Categories.Remove(category);
+            await _db.SaveChangesAsync();
+        }
+    }
+}