feat: Update Node.js version to 18.16.1 in .nvmrc and add CLAUDE.md for project settings

.claude/CLAUDE.md

@@ -0,0 +1,13 @@
+# Claude Code Settings for Bigcapital
+
+## Node.js Version
+
+Always use Node.js 18.16.1 for this project. Before running any npm/pnpm/node commands:
+
+```bash
+nvm use 18.16.1
+```
+
+## Package Manager
+
+Use `pnpm` for this project.

.nvmrc

@@ -1 +1 @@
-v14.20
+18.16.1