Improve: Recategorize page error display and provider detection

Add error message alert for failed proposal applications. Derive AI
provider name from model prefix instead of separate config key.

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

MoneyMap/Pages/Recategorize.cshtml

@@ -18,6 +18,13 @@
         <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
     </div>
 }
+@if (!string.IsNullOrEmpty(Model.ErrorMessage))
+{
+    <div class="alert alert-danger alert-dismissible fade show" role="alert">
+        @Model.ErrorMessage
+        <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
+    </div>
+}
 
 <div class="row mb-4">
     <div class="col-md-4">

MoneyMap/Pages/Recategorize.cshtml.cs

@@ -26,11 +26,24 @@ namespace MoneyMap.Pages
         }
 
         public RecategorizeStats Stats { get; set; } = new();
-        public string AIProvider => _config["AI:CategorizationProvider"] ?? "OpenAI";
+        public string AIProvider
+        {
+            get
+            {
+                var model = _config["AI:ReceiptParsingModel"] ?? "gpt-4o-mini";
+                if (model.StartsWith("llamacpp:", StringComparison.OrdinalIgnoreCase)) return "LlamaCpp";
+                if (model.StartsWith("ollama:", StringComparison.OrdinalIgnoreCase)) return "Ollama";
+                if (model.StartsWith("claude-", StringComparison.OrdinalIgnoreCase)) return "Anthropic";
+                return "OpenAI";
+            }
+        }
 
         [TempData]
         public string? SuccessMessage { get; set; }
 
+        [TempData]
+        public string? ErrorMessage { get; set; }
+
         public async Task OnGetAsync()
         {
             await LoadStatsAsync();