Fix HF dataset import internal error and training SQLite readiness.

Wrap AssistentImportHfDataset in try/catch, batch inserts in a transaction, clearer HF rows errors for gated datasets, EnsureTrainingReady with actionable message, and friendlier training UI errors instead of generic internal error.

Co-authored-by: Cursor <cursoragent@cursor.com>

AssistentTraining.Agent.cs

@@ -25,14 +25,21 @@ public partial class SwarmAssistentExtension
     public async Task<JObject> AssistentGetDatasetAgentSettings(Session session)
     {
         await Task.CompletedTask;
-        JObject settings = Config.LoadTrainingAgent();
-        return new JObject
+        try
         {
-            ["success"] = true,
-            ["settings"] = settings,
-            ["linked"] = Memory.CountAgentLinkedTrainSamples(),
-            ["approved"] = Memory.CountTrainSamples("approved"),
-        };
+            JObject settings = Config.LoadTrainingAgent();
+            return new JObject
+            {
+                ["success"] = true,
+                ["settings"] = settings,
+                ["linked"] = Memory.CountAgentLinkedTrainSamples(),
+                ["approved"] = Memory.CountTrainSamples("approved"),
+            };
+        }
+        catch (Exception ex)
+        {
+            return new JObject { ["error"] = ex.Message };
+        }
     }
 
     public async Task<JObject> AssistentSaveDatasetAgentSettings(Session session, JObject settings)