fix(cli): improve config init and config list UX

[whoAbhishekSah]

Summary

The frontier config subcommands have UX issues that make it unclear what's happening:

1. frontier config init gives no feedback

Running frontier config init creates a file at ~/.config/frontier.yaml but prints nothing to stdout. It should confirm the file was created and show the path.

Expected behavior:

Config file created at ~/.config/frontier.yaml

2. frontier config list shows empty {}

After running config init, frontier config list outputs just {} — even though a config file exists. It should either display the config values from the file or indicate that defaults are being used.

Current:

$ frontier config list
{}

Expected: Show the actual config values or a helpful message.

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