feat: add config command to show config path

[devKobe24]

Closes #45

Summary

Adds a config command that prints the config file path and current settings.
The access token value is never printed — only whether it is set.

Usage

$ hackmd-cli config
Config file: /Users/you/.hackmd/config.json
hackmdAPIEndpointURL: https://api.hackmd.io/v1
accessToken: (set)

$ hackmd-cli config --path
/Users/you/.hackmd/config.json

Tests

• Added test/config-command.test.ts, including a check that the token value is never printed
• pnpm test: all passing, lint clean (Node 24)