Enforce pnpm-only usage: Remove npm lock file and update documentation

.github/copilot-instructions.md

@@ -84,7 +84,10 @@ When working with number-to-text conversion, follow these Vietnamese language co
 - Only add devDependencies for tooling
 
 ### Package Manager
-- Use **pnpm** (not npm or yarn)
+- **ONLY use pnpm** - npm and yarn are NOT allowed in this repository
+- Never use `npm install` or `yarn install` commands
+- All dependency management must be done with `pnpm` commands
+- Lock files: Only `pnpm-lock.yaml` is allowed (package-lock.json and yarn.lock are ignored)
 - Workspaces are configured for the `docs` subdirectory
 
 ## Security Best Practices

.gitignore

@@ -124,3 +124,7 @@ dist
 
 # IDEs
 .idea/
+
+# Lock files for other package managers (only use pnpm)
+package-lock.json
+yarn.lock

README.md

@@ -19,7 +19,7 @@
 ## Installation
 
 ```bash
-npm install vn-number
+pnpm add vn-number
 ```
 
 ```bash