feat: add user-defined safe commands configuration and approval logic #380 (#386)

This pull request adds a feature that allows users to configure
auto-approved commands via a `safeCommands` array in the configuration
file.

## Related Issue
#380 

## Changes
- Added loading and validation of the `safeCommands` array in
`src/utils/config.ts`
- Implemented auto-approval logic for commands matching `safeCommands`
prefixes in `src/approvals.ts`
- Added test cases in `src/tests/approvals.test.ts` to verify
`safeCommands` behavior
- Updated documentation with examples and explanations of the
configuration

README.md

@@ -288,6 +288,9 @@ Codex looks for config files in **`~/.codex/`**.
 model: o4-mini # Default model
 fullAutoErrorMode: ask-user # or ignore-and-continue
 notify: true # Enable desktop notifications for responses
+safeCommands:
+  - npm test # Automatically approve npm test
+  - yarn lint # Automatically approve yarn lint
 ```
 
 You can also define custom instructions: