feat: Remove 9 low-value tools and consolidate n8n_health_check (v2.25.0)

Telemetry-driven tool cleanup to improve API clarity:

**Removed Tools (9):**
- list_nodes - Use search_nodes instead
- list_ai_tools - Use search_nodes with isAITool filter
- list_tasks - Low usage (0.02%)
- get_database_statistics - Use n8n_health_check
- list_templates - Use search_templates or get_templates_for_task
- get_node_as_tool_info - Documented in get_node
- validate_workflow_connections - Use validate_workflow
- validate_workflow_expressions - Use validate_workflow
- n8n_list_available_tools - Use n8n_health_check
- n8n_diagnostic - Merged into n8n_health_check

**Consolidated Tool:**
- n8n_health_check now supports mode='diagnostic' for detailed troubleshooting

**Tool Count:**
- Before: 38 tools
- After: 31 tools (18% reduction)

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

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

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

tests/unit/mcp/handlers-n8n-manager.test.ts

@@ -1068,14 +1068,14 @@ describe('handlers-n8n-manager', () => {
         },
         toolsAvailability: {
           documentationTools: {
-            count: 22,
+            count: 14,
             enabled: true,
           },
           managementTools: {
-            count: 16,
+            count: 17,
             enabled: true,
           },
-          totalAvailable: 38,
+          totalAvailable: 31,
         },
       });