feat(completion): Implement completion commands

[jongwooo]

This pull request adds shell completion support to the morpherctl CLI, allowing users to easily generate completion scripts for bash, zsh, fish, and powershell. The changes include a new completion command, supporting logic for script generation, and corresponding tests to ensure correctness.

Shell completion feature:

• Added a new completion subcommand to morpherctl that generates shell completion scripts for bash, zsh, fish, and powershell, with usage instructions and argument validation in cmd/completion/completion.go.
• Integrated the completion command into the root command by importing and registering it in cmd/root.go. [1] [2]

Completion logic and testing:

• Implemented shell completion script generation logic and supported shell listing in internal/completion/completion.go.
• Added unit tests for completion generation and supported shells in internal/completion/completion_test.go.

[Copilot]

Pull Request Overview

This pull request implements shell completion support for the morpherctl CLI tool, enabling users to generate completion scripts for bash, zsh, fish, and powershell shells.

• Adds a new completion command with argument validation and usage instructions
• Implements completion script generation logic with support for four major shells
• Includes comprehensive unit tests for the completion functionality

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
cmd/completion/completion.go	Defines the completion command with usage examples and shell validation
internal/completion/completion.go	Implements core completion generation logic and supported shells listing
internal/completion/completion_test.go	Provides unit tests for completion generation and shell support validation
cmd/root.go	Integrates the completion command into the root CLI command structure

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