Add document resource to n8n node and MCP sendSigningNotifications tool

Add a complete document resource to the n8n node with 21 operations
covering documents, versions, and signatures — matching the MCP
specification. Also add the sendSigningNotifications tool to the MCP
API for triggering pending signature reminders.

n8n operations: create, get, getAll, update, delete, archive,
unarchive, getVersion, getAllVersions, createDraftVersion,
updateVersion, deleteDraftVersion, publishMajorVersion,
publishMinorVersion, requestApproval, voidApproval, getSignature,
getAllSignatures, requestSignature, cancelSignature,
sendSigningNotifications.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

packages/n8n-node/nodes/Probo/Probo.node.ts

@@ -96,6 +96,11 @@ export class Probo implements INodeType {
 						value: 'datum',
 						description: 'Manage data',
 					},
+					{
+						name: 'Document',
+						value: 'document',
+						description: 'Manage documents, versions, and signatures',
+					},
 					{
 						name: 'Execute',
 						value: 'execute',