feat: Complete Skill #2 - n8n MCP Tools Expert

Implements comprehensive guidance for using n8n-mcp MCP tools effectively.
This is the HIGHEST PRIORITY skill that addresses the 20% MCP tool failure rate.

Files created:
- 5 evaluations testing tool selection, nodeType formats, validation, and smart parameters
- SKILL.md (505 lines) - Core tool usage guide with telemetry insights
- SEARCH_GUIDE.md (243 lines) - Node discovery tools (search, essentials vs info)
- VALIDATION_GUIDE.md (377 lines) - Configuration validation and auto-sanitization
- WORKFLOW_GUIDE.md (385 lines) - Workflow management with 15 operation types
- README.md - Skill metadata emphasizing highest priority

Key features:
- Tool selection guide with success rates (search_nodes 99.9%, get_node_essentials 91.7%)
- nodeType format distinction (nodes-base.* vs n8n-nodes-base.*)
- Validation profiles explained (minimal/runtime/ai-friendly/strict)
- Smart parameters for IF/Switch nodes (branch="true", case=0)
- Auto-sanitization system for operator structures
- Telemetry insights (56s between edits, 18s search→essentials, 23s+58s validate→fix)
- AI connection types (8 types documented)

Total: ~1,650 lines across 10 files

Based on analysis of 447,557 real MCP tool usage events.

🤖 Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

evaluations/mcp-tools/eval-004-essentials-vs-info.json

@@ -0,0 +1,25 @@
+{
+  "id": "mcp-004",
+  "skills": ["n8n-mcp-tools-expert"],
+  "query": "Should I use get_node_info or get_node_essentials to understand how to configure a node? What's the difference?",
+  "expected_behavior": [
+    "Strongly recommends get_node_essentials for most cases",
+    "Explains size difference (5KB vs 100KB+)",
+    "Explains success rate difference (91.7% vs 80%)",
+    "Lists when to use get_node_info (debugging complex issues, need full schema)",
+    "Provides performance comparison (<10ms vs slower)",
+    "References the 20% failure rate for get_node_info",
+    "Shows examples of both tool calls"
+  ],
+  "baseline_without_skill": {
+    "likely_response": "May assume more data is better, unlikely to know performance and reliability differences",
+    "expected_quality": "Low - would not understand the critical difference"
+  },
+  "with_skill_expected": {
+    "response_quality": "High - clear recommendation with data-driven reasoning",
+    "uses_skill_content": true,
+    "recommends_essentials": true,
+    "explains_trade_offs": true,
+    "provides_both_examples": true
+  }
+}