feat: add tab completion support for CLI commands

[jeffreyaven]

This PR implements tab completion functionality for the stackql-deploy CLI as requested in issue #65.

Changes

• Added new completion command to generate shell completion scripts
• Support for bash, zsh, fish, and PowerShell shells
• Leverages Click's built-in shell completion functionality
• Updated README with detailed setup instructions
• Enables tab completion for all subcommands and flags

Usage

Users can enable tab completion by:

1. Running stackql-deploy completion <shell> to get setup instructions
2. Adding the appropriate line to their shell config file
3. Restarting their terminal or sourcing the config

Resolves #65

🤖 Generated with Claude Code

[jeffreyaven]

@claude can you fix https://github.com/stackql/stackql-deploy/actions/runs/18422097076, ruff linting error

[claude]

Claude finished @jeffreyaven's task —— View job

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✅ Fixed ruff linting error

• Read the changed files to understand the implementation
• Check for repo-specific instructions in CLAUDE.md
• Identify the specific ruff linting error
• Fix the linting error (line length issue in completion command)
• Commit and push the changes

Fixed: Line 389 in stackql_deploy/cli.py exceeded the 120 character limit configured in ruff settings. I broke the long @click.argument() decorator into multiple lines for better readability and compliance with the linting rules.

The fix has been committed and pushed to the PR branch. The GitHub Actions workflow should now pass the ruff linting checks.

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