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>

CHANGELOG.md

@@ -7,6 +7,29 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.31.5] - 2026-01-02
+
+### Added
+
+**MCP Tool Annotations (PR #512)**
+
+Added MCP tool annotations to all 20 tools following the [MCP specification](https://spec.modelcontextprotocol.io/specification/2025-03-26/server/tools/#annotations). These annotations help AI assistants understand tool behavior and capabilities.
+
+**Annotations added:**
+- `title`: Human-readable name for each tool
+- `readOnlyHint`: True for tools that don't modify state (11 tools)
+- `destructiveHint`: True for delete operations (3 tools)
+- `idempotentHint`: True for operations that produce same result when called repeatedly (14 tools)
+- `openWorldHint`: True for tools accessing external n8n API (13 tools)
+
+**Documentation tools** (7): All marked `readOnlyHint=true`, `idempotentHint=true`
+- `tools_documentation`, `search_nodes`, `get_node`, `validate_node`, `get_template`, `search_templates`, `validate_workflow`
+
+**Management tools** (13): All marked `openWorldHint=true`
+- Read-only: `n8n_get_workflow`, `n8n_list_workflows`, `n8n_validate_workflow`, `n8n_health_check`
+- Idempotent updates: `n8n_update_full_workflow`, `n8n_update_partial_workflow`, `n8n_autofix_workflow`
+- Destructive: `n8n_delete_workflow`, `n8n_executions` (delete action), `n8n_workflow_versions` (delete/truncate)
+
 ## [2.31.4] - 2026-01-02
 
 ### Fixed