feat: add MCP tool annotations to all 20 tools (#512)

* feat: add MCP tool annotations to all 20 tools

Add MCP tool annotations per specification to help AI assistants
understand tool behavior and capabilities.

Documentation tools (7):
- tools_documentation, search_nodes, get_node, validate_node,
  get_template, search_templates, validate_workflow
- All marked readOnlyHint=true (local database queries)

Management tools (13):
- n8n_create_workflow, n8n_get_workflow, n8n_update_full_workflow,
  n8n_update_partial_workflow, n8n_delete_workflow, n8n_list_workflows,
  n8n_validate_workflow, n8n_autofix_workflow, n8n_test_workflow,
  n8n_executions, n8n_health_check, n8n_workflow_versions,
  n8n_deploy_template
- All marked openWorldHint=true (n8n API access)
- Destructive operations (delete_workflow, executions delete,
  workflow_versions delete/truncate) marked destructiveHint=true

Annotations follow MCP spec:
https://spec.modelcontextprotocol.io/specification/2025-03-26/server/tools/#annotations

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* feat: add idempotentHint to all read-only tools

Adds idempotentHint: true annotation to all read-only tools that produce
the same output when called multiple times:
- 7 documentation tools (tools.ts)
- 4 management tools (tools-n8n-manager.ts): n8n_get_workflow,
  n8n_list_workflows, n8n_validate_workflow, n8n_health_check

Also adds trailing newline to tools-n8n-manager.ts.

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

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* feat: add idempotentHint to update operations, bump to 2.31.5

Adds idempotentHint: true to update operations that produce the same
result when called repeatedly with the same arguments:
- n8n_update_full_workflow
- n8n_update_partial_workflow
- n8n_autofix_workflow

Also bumps version to 2.31.5 and updates CHANGELOG.md with complete
documentation of all MCP tool annotations added in this PR.

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

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: triepod-ai <noreply@github.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: Romuald Członkowski <romualdczlonkowski@MacBook-Pro-Romuald.local>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.31.4",
+  "version": "2.31.5",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",