Clean up LLM digest provider errors

lib/features/ai_digest/application/llm_digest_orchestrator.dart

@@ -2,6 +2,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:relationship_saver/app/data/relationship_repository.dart';
 import 'package:relationship_saver/app/state/local_data_state.dart';
 import 'package:relationship_saver/core/llm/llm_config.dart';
+import 'package:relationship_saver/core/llm/llm_service.dart';
 import 'package:relationship_saver/features/ai_digest/application/ai_digest_notifier.dart';
 import 'package:relationship_saver/features/ai_digest/application/ai_digest_response_parser.dart';
 import 'package:relationship_saver/features/ai_digest/application/anonymized_llm_context_builder.dart';
@@ -185,11 +186,12 @@ class LlmDigestOrchestrator {
         createdDraftCount: parsed.drafts.length,
       );
     } catch (error) {
-      await _markFailure('$error');
+      final String reason = _digestFailureReason(error);
+      await _markFailure(reason);
       return LlmDigestRunResult(
         started: true,
         completed: false,
-        reason: '$error',
+        reason: reason,
       );
     }
   }
@@ -232,6 +234,13 @@ class LlmDigestOrchestrator {
   }
 }
 
+String _digestFailureReason(Object error) {
+  if (error is LlmProviderException) {
+    return error.message;
+  }
+  return '$error';
+}
+
 const String _systemPrompt = '''
 You create private relationship-maintenance digest suggestions.
 The input contains pseudonymous people only. Never ask for or invent names.