feat: Semantische Suche über Chat-History (memory_search)

- Lokales Embedding-Model (all-MiniLM-L6-v2, ONNX, CPU)
- EmbeddingService: WordPiece-Tokenizer + Mean Pooling (384 Dim)
- VectorSearchService: SQLite-basierte Vektor-Speicherung + Cosine Similarity
- EmbeddingBackgroundService: Backfill bestehender Messages + Live-Queue
- Neues Tool memory_search: Semantische Suche über alle Sessions (inkl. archivierte)
- ~9000 Messages embedded, Suche über komplette Chat-History

Services/ToolService.cs

@@ -33,7 +33,7 @@ public class ToolService
     private static readonly HashSet<string> ReadOnlyToolNames = new HashSet<string>
     {
         "read_file", "list_files", "glob", "grep", "execute", "todo_write",
-        "memory_read", "memory_write", "memory_list",
+        "memory_read", "memory_write", "memory_list", "memory_search",
         "remote_execute", AskUserChoiceToolName
     };
 
@@ -54,7 +54,7 @@ public class ToolService
         return filtered.ToArray();
     }
 
-    public object[] GetToolDefinitions(bool includeFileTools = false, bool includeMemory = false, bool includeUserChoice = true, bool includeRemote = false)
+    public object[] GetToolDefinitions(bool includeFileTools = false, bool includeMemory = false, bool includeUserChoice = true, bool includeRemote = false, bool includeMemorySearch = false)
     {
         var allTools = new List<object>();
         if (includeUserChoice)
@@ -63,6 +63,8 @@ public class ToolService
             allTools.AddRange(GetFileTools());
         if (includeMemory)
             allTools.AddRange(GetMemoryToolDefinitions());
+        if (includeMemorySearch)
+            allTools.Add(GetMemorySearchTool());
         if (includeRemote)
             allTools.Add(GetRemoteExecuteTool());
         return allTools.ToArray();
@@ -264,6 +266,25 @@ public class ToolService
         };
     }
 
+    private object GetMemorySearchTool()
+    {
+        return new
+        {
+            name = "memory_search",
+            description = "Semantische Suche über alle vergangenen Chat-Nachrichten (inklusive archivierter Sessions). Findet relevante Informationen aus früheren Gesprächen anhand von Bedeutung, nicht exakten Wörtern. Nutze dies wenn du Kontext aus vergangenen Interaktionen brauchst.",
+            input_schema = new
+            {
+                type = "object",
+                properties = new Dictionary<string, object>
+                {
+                    ["query"] = new { type = "string", description = "Suchanfrage – beschreibe wonach du suchst (z.B. 'Druckerproblem letzte Woche', 'Server-Migration Konfiguration')" },
+                    ["top_n"] = new { type = "integer", description = "Anzahl der Ergebnisse (Default: 10, Max: 30)" }
+                },
+                required = new[] { "query" }
+            }
+        };
+    }
+
     private object GetRemoteExecuteTool()
     {
         return new
@@ -333,7 +354,7 @@ public class ToolService
         };
     }
 
-    public async Task<string> ExecuteTool(string name, JsonElement input, string workspace, MemoryService memoryService = null, string agentId = null, CancellationToken cancellationToken = default, RemoteConnectionManager remoteMgr = null, string sessionId = null)
+    public async Task<string> ExecuteTool(string name, JsonElement input, string workspace, MemoryService memoryService = null, string agentId = null, CancellationToken cancellationToken = default, RemoteConnectionManager remoteMgr = null, string sessionId = null, VectorSearchService vectorSearch = null)
     {
         switch (name)
         {
@@ -617,6 +638,29 @@ public class ToolService
                 var files = memoryService.ListMemoryFiles(agentId, subPath);
                 return files.Count == 0 ? "(keine Memory-Dateien vorhanden)" : string.Join("\n", files);
             }
+            case "memory_search":
+            {
+                if (vectorSearch == null)
+                    return "Fehler: Semantische Suche nicht verfügbar";
+                var query = input.GetProperty("query").GetString() ?? "";
+                var topN = input.TryGetProperty("top_n", out var tn) ? tn.GetInt32() : 10;
+                if (topN > 30) topN = 30;
+                if (topN < 1) topN = 1;
+                var results = await vectorSearch.SearchAsync(query, agentId, topN);
+                if (results.Count == 0)
+                    return "Keine relevanten Ergebnisse gefunden.";
+                var sb = new StringBuilder();
+                sb.AppendLine($"Gefunden: {results.Count} relevante Einträge\n");
+                for (int i = 0; i < results.Count; i++)
+                {
+                    var r = results[i];
+                    var date = DateTime.TryParse(r.CreatedAt, out var dt) ? dt.ToString("yyyy-MM-dd HH:mm") : r.CreatedAt;
+                    sb.AppendLine($"[{i + 1}] Score: {r.Score:F2} | {r.Role} | {date} | Session: {r.SessionId}");
+                    sb.AppendLine(r.TextPreview);
+                    sb.AppendLine();
+                }
+                return sb.ToString().TrimEnd();
+            }
             case "remote_execute":
             {
                 if (remoteMgr == null || string.IsNullOrEmpty(sessionId))