refactor: Backend-Deduplizierung – Parameter-Objekte, Shared Helpers, KeyCheckDispatcher

- ToolDefinitionOptions + ToolExecutionContext ersetzen lange Parameterlisten in ToolService
- AppendToLastMessage-Helper in ChatService eliminiert 5x duplizierte Logik
- OpenAiService: ResolveProviderConfig + BuildApiMessages + ConvertToOpenAiTools statt doppeltem Code
- Tool-Definitionen aus einer Quelle (Anthropic→OpenAI Konvertierung statt hardcodierter Liste)
- KeyCheckDispatcher zentralisiert Key-Check-Dispatch (ApiKeysEndpoint, KeyScanner, GitHubEventScanner)

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

Services/AnthropicService.Streaming.cs

@@ -589,7 +589,14 @@ public partial class AnthropicService
 
                             string toolResult;
                             bool isError = false;
-                            try { toolResult = await _toolService.ExecuteTool(currentToolName, inputEl, workspace, _memoryService, agentId, workCt, remoteMgr: remoteMgr, sessionId: sessionId, vectorSearch: _vectorSearch, embeddingBg: _embeddingBg, db: _db, chatService: _chatService, anthropicService: this, openAiService: _openAiService, userId: userId, telegramService: _telegramService, apiToken: apiToken); }
+                            try { toolResult = await _toolService.ExecuteTool(currentToolName, inputEl, new ToolExecutionContext
+                            {
+                                Workspace = workspace, MemoryService = _memoryService, AgentId = agentId,
+                                CancellationToken = workCt, RemoteMgr = remoteMgr, SessionId = sessionId,
+                                VectorSearch = _vectorSearch, EmbeddingBg = _embeddingBg, Db = _db,
+                                ChatService = _chatService, AnthropicService = this, OpenAiService = _openAiService,
+                                UserId = userId, TelegramService = _telegramService, ApiToken = apiToken
+                            }); }
                             catch (OperationCanceledException) { throw; }
                             catch (Exception ex) { toolResult = $"Fehler: {ex.Message}"; isError = true; }