feat: add cli custom tool name support with tests

[5angar1us]

Custom CLI Tool Support for Skill Invocation

Summary: Added support for custom CLI tool names in AGENTS.md generation, allowing users to specify the tool name that agents will use to invoke openskills.

What: Added --cli-tool flag to sync command to customize the CLI tool name used in AGENTS.md.

Why:

• Different AI agents may use different tool invocation methods (e.g., Shell, Execute, Command) instead of the default Bash
• Users need flexibility to configure the tool name according to their agent's requirements
• Maintains compatibility with existing default behavior while adding customization options

Implementation:

• Added --cli-tool <name> flag to the sync command
• Modified generateSkillsXml function in src/utils/agents-md.ts to accept and use custom tool name
• Updated command-line interface to accept the new option
• Default behavior remains unchanged (uses 'Bash' as default tool name)
• Updated documentation in README.md to reflect the new functionality

Testing:

• Verified that the default behavior remains unchanged when flag is not used
• Confirmed that AGENTS.md is generated with the correct custom tool name
• All existing tests continue to pass

Usage:

# Default behavior (uses Bash as tool name)
openskills sync

# With custom CLI tool name
openskills sync --cli-tool Shell