Seed default category mappings on application startup

Added automatic seeding of default category mappings to ensure the
transaction categorizer has patterns to match against. This fixes the
issue where all transactions appeared as uncategorized during preview
because the CategoryMappings table was empty.

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

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

MoneyMap/Program.cs

@@ -10,6 +10,15 @@ builder.Services.AddRazorPages();
 builder.Services.AddDbContext<MoneyMapContext>(options =>
     options.UseSqlServer(builder.Configuration.GetConnectionString("MoneyMapDb")));
 
+// Add session support
+builder.Services.AddDistributedMemoryCache();
+builder.Services.AddSession(options =>
+{
+    options.IdleTimeout = TimeSpan.FromMinutes(30);
+    options.Cookie.HttpOnly = true;
+    options.Cookie.IsEssential = true;
+});
+
 // Add the new services here
 builder.Services.AddScoped<ITransactionImporter, TransactionImporter>();
 builder.Services.AddScoped<ICardResolver, CardResolver>();
@@ -25,6 +34,13 @@ builder.Services.AddHttpClient<IReceiptParser, OpenAIReceiptParser>();
 
 var app = builder.Build();
 
+// Seed default category mappings on startup
+using (var scope = app.Services.CreateScope())
+{
+    var categorizer = scope.ServiceProvider.GetRequiredService<ITransactionCategorizer>();
+    await categorizer.SeedDefaultMappingsAsync();
+}
+
 // Configure the HTTP request pipeline.
 if (!app.Environment.IsDevelopment())
 {
@@ -37,6 +53,8 @@ app.UseStaticFiles();
 
 app.UseRouting();
 
+app.UseSession();
+
 app.UseAuthorization();
 
 app.MapRazorPages();