Hide carapace internal command from completions

[M09Ic]

Background

Carapace injects an internal _carapace command for shell completion plumbing. In an interactive console, that implementation detail should not be offered as a normal user command.

Approach

• Hide _carapace recursively after carapace.Gen has initialized completion state.
• Filter _carapace out while converting carapace values into readline completions.
• Keep the change limited to the completion path.

Tests

• Added a regression test with an explicit _carapace subcommand.
• Verified the command is hidden and not returned as a completion value.
• Ran go test ./...