fix: raise session timeout default, fix VS Code MCP compatibility (#674)

* fix: raise session timeout default and fix VS Code MCP compatibility (#626, #600, #611)

- #626: Raise SESSION_TIMEOUT_MINUTES default from 5 to 30 minutes.
  Complex editing sessions easily exceed 5 min between LLM calls.

- #600: Add z.preprocess(tryParseJson, ...) to operations parameter
  in n8n_update_partial_workflow. VS Code extension sends arrays as
  JSON strings.

- #611: Strip undefined values from tool args via JSON round-trip
  before Zod validation. VS Code sends explicit undefined which
  Zod's .optional() rejects.

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor: deduplicate tryParseJson — export from handlers-n8n-manager

tryParseJson was duplicated in handlers-workflow-diff.ts. Now imported
from handlers-n8n-manager.ts where it was already defined. Updated
test mock to use importOriginal so the real function is available.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/mcp/server.ts

@@ -748,6 +748,13 @@ export class N8NDocumentationMCPServer {
       // tool's inputSchema as the source of truth.
       processedArgs = this.coerceStringifiedJsonParams(name, processedArgs);
 
+      // Strip undefined values from args (#611) — VS Code extension sends
+      // explicit undefined values which Zod's .optional() rejects.
+      // Removing them makes Zod treat them as missing (which .optional() allows).
+      if (processedArgs) {
+        processedArgs = JSON.parse(JSON.stringify(processedArgs));
+      }
+
       try {
         logger.debug(`Executing tool: ${name}`, { args: processedArgs });
         const startTime = Date.now();