fix: use 'updates' property consistently in updateNode operations

- Changed UpdateNodeOperation interface to use 'updates' instead of 'changes'
- Updated UpdateConnectionOperation for consistency
- Fixed implementation in workflow-diff-engine.ts
- Updated Zod schema validation
- Fixed documentation and examples
- Updated tests to match new property name

This resolves GitHub issues #159 and #168 where partial workflow updates
were failing, forcing AI agents to fall back to expensive full updates.

🤖 Generated with Claude Code

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

src/mcp/handlers-workflow-diff.ts

@@ -21,7 +21,7 @@ const workflowDiffSchema = z.object({
     node: z.any().optional(),
     nodeId: z.string().optional(),
     nodeName: z.string().optional(),
-    changes: z.any().optional(),
+    updates: z.any().optional(),
     position: z.tuple([z.number(), z.number()]).optional(),
     // Connection operations
     source: z.string().optional(),