Add AI categorization with Ollama: settings, auto-classify on sync/import, and manual classify from Transactions

Adds local LLM-based transaction categorization using Ollama:
- Settings UI to configure Ollama URL, model, confidence threshold
- Auto-categorization during bank sync and file import
- Manual "Classify Uncategorized" button on Transactions screen that respects active filters
- Payee default category learning loop for classified transactions

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

src/Purrse.Core/Models/AiCategorizationSettings.cs

@@ -0,0 +1,16 @@
+namespace Purrse.Core.Models;
+
+public class AiCategorizationSettings
+{
+    public Guid Id { get; set; }
+    public Guid UserId { get; set; }
+    public bool IsEnabled { get; set; }
+    public string OllamaUrl { get; set; } = "http://localhost:11434";
+    public string ModelName { get; set; } = "llama3.1:8b";
+    public double ConfidenceThreshold { get; set; } = 0.7;
+    public int TimeoutSeconds { get; set; } = 30;
+    public bool UpdatePayeeDefaults { get; set; } = true;
+    public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+
+    public User User { get; set; } = null!;
+}

src/Purrse.Core/Models/User.cs

@@ -14,4 +14,5 @@ public class User
     public ICollection<Account> Accounts { get; set; } = new List<Account>();
     public ICollection<SyncConnection> SyncConnections { get; set; } = new List<SyncConnection>();
     public BankSyncSettings? BankSyncSettings { get; set; }
+    public AiCategorizationSettings? AiCategorizationSettings { get; set; }
 }