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-003-validation-workflow.json

@@ -0,0 +1,25 @@
+{
+  "id": "mcp-003",
+  "skills": ["n8n-mcp-tools-expert"],
+  "query": "I've created a Slack node configuration and want to make sure it's valid before deploying. Walk me through the validation process using n8n-mcp tools.",
+  "expected_behavior": [
+    "Recommends validate_node_operation tool",
+    "Explains validation profiles (minimal, runtime, ai-friendly, strict)",
+    "Recommends 'runtime' profile for pre-deployment",
+    "Shows complete validation syntax with all parameters",
+    "Explains validation loop pattern (validate → fix → validate again)",
+    "References VALIDATION_GUIDE.md",
+    "Mentions 23s avg thinking time, 58s avg fixing time from telemetry"
+  ],
+  "baseline_without_skill": {
+    "likely_response": "May suggest testing the workflow or checking documentation, unlikely to know validation tools and profiles",
+    "expected_quality": "Medium - might guess at validation but miss profile options"
+  },
+  "with_skill_expected": {
+    "response_quality": "High - complete validation workflow with profiles",
+    "uses_skill_content": true,
+    "recommends_correct_profile": true,
+    "shows_validation_loop": true,
+    "explains_error_handling": true
+  }
+}