feat: AutoContext-Suche grundlegend verbessern + Embedding-Debug-Tool

Hybrid-Suche (Vektor + FTS5-Keyword), Recency-Boost, Query-Erweiterung
(letzte 2-3 User-Messages), Chunk-Overlapping, FullText-Speicherung,
konfigurierbares Embedding-Modell/MaxSeqLen, deduplizierter AutoContext-
Code (Streaming + CLI shared), Admin-Diagnose-Seite mit Re-Embed-Funktion.
Threshold von 0.45 auf 0.35 gesenkt (Hybrid-Suche ist präziser).

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

Services/EmbeddingBackgroundService.cs

@@ -23,6 +23,7 @@ public class EmbeddingBackgroundService : BackgroundService
     readonly ConcurrentQueue<EmbeddingJob> _queue = new();
     readonly SemaphoreSlim _signal = new(0);
     readonly string _dataPath;
+    volatile bool _reEmbedRequested;
 
     public EmbeddingBackgroundService(VectorSearchService vectorSearch, EmbeddingService embedding, string dbPath)
     {
@@ -32,6 +33,13 @@ public class EmbeddingBackgroundService : BackgroundService
         _dataPath = Path.GetDirectoryName(dbPath);
     }
 
+    /// <summary>Triggers a full re-embedding of all data.</summary>
+    public void TriggerReEmbed()
+    {
+        _reEmbedRequested = true;
+        _signal.Release();
+    }
+
     /// <summary>Enqueue eine neue Message zum Embedden.</summary>
     public void Enqueue(long messageId, string chainId, string sessionId, string agentId, string role, string text)
     {
@@ -85,6 +93,17 @@ public class EmbeddingBackgroundService : BackgroundService
                         Console.WriteLine($"[EmbeddingBG] Error embedding job: {ex.Message}");
                     }
                 }
+
+                // Check for re-embed request
+                if (_reEmbedRequested)
+                {
+                    _reEmbedRequested = false;
+                    Console.WriteLine("[EmbeddingBG] Re-embedding triggered...");
+                    await _vectorSearch.ReEmbedAllAsync();
+                    await BackfillAsync(ct);
+                    await BackfillMemoryFilesAsync(ct);
+                    Console.WriteLine("[EmbeddingBG] Re-embedding complete.");
+                }
             }
             catch (OperationCanceledException) { break; }
         }