fix: validation bugs — If/Switch version check, Set false positive, bare expressions (#675, #676, #677) (#678)

- #675: Wire `validateConditionNodeStructure` into `WorkflowValidator` with
  version-conditional checks (If v2.2+ requires options, v2.0-2.1 validates
  operators, v1.x skipped; Switch v3.2+ requires options)
- #676: Fix `validateSet` to check `assignments.assignments` (v3+) alongside
  `config.values` (v1/v2), eliminating false positive warnings
- #677: Add anchored heuristic pre-pass in `ExpressionValidator` detecting bare
  `$json`, `$node`, `$input`, `$execution`, `$workflow`, `$prevNode`, `$env`,
  `$now`, `$today`, `$itemIndex`, `$runIndex` references missing `={{ }}`

25 new tests across 3 test files.

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

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.41.3",
+  "version": "2.41.4",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",