Refactor: Add structured error logging to TransactionAICategorizer

- Add ILogger for proper error logging
- Differentiate between HTTP, JSON parsing, and general errors
- Log errors with descriptive messages for debugging

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

MoneyMap/Services/TransactionAICategorizer.cs

@@ -19,12 +19,18 @@ public class TransactionAICategorizer : ITransactionAICategorizer
     private readonly HttpClient _httpClient;
     private readonly MoneyMapContext _db;
     private readonly IConfiguration _config;
+    private readonly ILogger<TransactionAICategorizer> _logger;
 
-    public TransactionAICategorizer(HttpClient httpClient, MoneyMapContext db, IConfiguration config)
+    public TransactionAICategorizer(
+        HttpClient httpClient,
+        MoneyMapContext db,
+        IConfiguration config,
+        ILogger<TransactionAICategorizer> logger)
     {
         _httpClient = httpClient;
         _db = db;
         _config = config;
+        _logger = logger;
     }
 
     public async Task<AICategoryProposal?> ProposeCategorizationAsync(Transaction transaction)
@@ -205,8 +211,19 @@ Return ONLY valid JSON, no additional text.";
 
             return result;
         }
-        catch
+        catch (HttpRequestException ex)
         {
+            _logger.LogError(ex, "OpenAI API request failed: {Message}", ex.Message);
+            return null;
+        }
+        catch (JsonException ex)
+        {
+            _logger.LogError(ex, "Failed to parse OpenAI response JSON: {Message}", ex.Message);
+            return null;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Unexpected error calling OpenAI API: {Message}", ex.Message);
             return null;
         }
     }