feat: add skills doctor command for agent diagnostics

[anthony-maio]

Adds a diagnostic command that outputs system info (OS, Node, CLI version) and lists all detected agents with their resolved project/global paths. Helps users and maintainers quickly triage "skill not loading" issues.

[vercel]

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[Copilot]

Pull request overview

This PR adds a new skills doctor diagnostic command to help users and maintainers quickly troubleshoot "skill not loading" issues by displaying system information and detected agent configurations. The command provides clear visibility into the CLI environment (OS, Node version, CLI version) and shows which agents are detected along with their resolved project and global skill paths.

Changes:

• Adds skills doctor command that outputs system diagnostics and agent detection information
• Integrates the new command into the CLI help text and banner
• Includes comprehensive test coverage for the new command

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/doctor.ts	Implements the diagnostic command with system info and agent detection logic
tests/doctor.test.ts	Adds test coverage for system information output, agent detection, exit codes, and logo display
src/cli.ts	Integrates the doctor command into the CLI router, help text, and banner

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[Copilot]

The import style is inconsistent with the rest of the codebase. All other files use named imports from 'os' without the 'node:' prefix (e.g., import { homedir } from 'os';). Consider changing to use named imports: import { type, release, arch } from 'os'; to maintain consistency.

[Copilot]

The imported type AgentType is not used in this file. The type is inferred from the return value of detectInstalledAgents(). Consider removing this unused import.

Suggested change

import type { AgentType } from './types.ts';