feat(api): add CategoriesController with list, mappings, and add-mapping endpoints

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

MoneyMap/Controllers/CategoriesController.cs

@@ -0,0 +1,88 @@
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using MoneyMap.Data;
+using MoneyMap.Models;
+using MoneyMap.Services;
+
+namespace MoneyMap.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+public class CategoriesController : ControllerBase
+{
+    private readonly MoneyMapContext _db;
+    private readonly ITransactionCategorizer _categorizer;
+    private readonly IMerchantService _merchantService;
+
+    public CategoriesController(MoneyMapContext db, ITransactionCategorizer categorizer, IMerchantService merchantService)
+    {
+        _db = db;
+        _categorizer = categorizer;
+        _merchantService = merchantService;
+    }
+
+    [HttpGet]
+    public async Task<IActionResult> List()
+    {
+        var categories = await _db.Transactions
+            .Where(t => t.Category != null && t.Category != "")
+            .GroupBy(t => t.Category!)
+            .Select(g => new { Category = g.Key, Count = g.Count(), TotalSpent = g.Where(t => t.Amount < 0).Sum(t => Math.Abs(t.Amount)) })
+            .OrderByDescending(x => x.Count)
+            .ToListAsync();
+
+        var uncategorized = await _db.Transactions
+            .CountAsync(t => t.Category == null || t.Category == "");
+
+        return Ok(new { Categories = categories, UncategorizedCount = uncategorized });
+    }
+
+    [HttpGet("mappings")]
+    public async Task<IActionResult> GetMappings([FromQuery] string? category = null)
+    {
+        var mappings = await _categorizer.GetAllMappingsAsync();
+
+        if (!string.IsNullOrWhiteSpace(category))
+            mappings = mappings.Where(m => m.Category.Equals(category, StringComparison.OrdinalIgnoreCase)).ToList();
+
+        var result = mappings.Select(m => new
+        {
+            m.Id,
+            m.Pattern,
+            m.Category,
+            m.MerchantId,
+            m.Priority
+        }).OrderBy(m => m.Category).ThenByDescending(m => m.Priority).ToList();
+
+        return Ok(result);
+    }
+
+    [HttpPost("mappings")]
+    public async Task<IActionResult> AddMapping([FromBody] CreateCategoryMappingRequest request)
+    {
+        int? merchantId = null;
+        if (!string.IsNullOrWhiteSpace(request.MerchantName))
+            merchantId = await _merchantService.GetOrCreateIdAsync(request.MerchantName);
+
+        var mapping = new CategoryMapping
+        {
+            Pattern = request.Pattern,
+            Category = request.Category,
+            MerchantId = merchantId,
+            Priority = request.Priority
+        };
+
+        _db.CategoryMappings.Add(mapping);
+        await _db.SaveChangesAsync();
+
+        return Ok(new { Created = true, mapping.Id, mapping.Pattern, mapping.Category, Merchant = request.MerchantName, mapping.Priority });
+    }
+}
+
+public class CreateCategoryMappingRequest
+{
+    public string Pattern { get; set; } = "";
+    public string Category { get; set; } = "";
+    public string? MerchantName { get; set; }
+    public int Priority { get; set; }
+}