Add variable validation features to README and CLI; implement linting and strict mode for environment variables in executor and linter. Enhance VSCode extension documentation for improved user guidance.

.vscode/extensions/playwrong-syntax/README.md

@@ -57,8 +57,24 @@ dump "login_page"
 - Unknown HTML elements
 - Generic element selectors
 - Semantic misuse (e.g., `click` on input fields)
+- **Undefined variables**: Variables that are not commonly defined environment variables
 
 ### Info
 - Environment variable usage
 - Command placement suggestions
-- Best practice tips 
+- Best practice tips
+
+## Variable Validation
+
+The extension now provides enhanced validation for environment variables:
+
+- **Common variables** like `$PASSWORD`, `$PASSWORDMAIL`, `$EMAIL`, `$USERNAME`, `$API_KEY`, `$TOKEN`, `$BASE_URL` show as info messages
+- **Undefined variables** that are not commonly defined show as warnings
+- Use the CLI with `--strict-variables` flag to treat undefined variables as errors during execution
+
+## CLI Integration
+
+The extension works with the PlayWrong CLI which supports:
+- `--lint` - Run linter before execution
+- `--strict` - Treat linter warnings as errors  
+- `--strict-variables` - Treat undefined variables as errors during execution