feat(onboarding): interactive AI-skills-first setup flow

[christso]

Objective

Design and implement an AI-skills-first interactive onboarding flow for AgentV, replacing current manual agentv init usage with guided setup in agent clients.

Why

Current onboarding still relies on a CLI command path and static instructions. We want a first-class interactive flow that runs through agent clients (Claude/Copilot/allagents-compatible surfaces), validates environment state, and guides users through setup decisions.

Scope

• Add an interactive TUI-style onboarding experience (or equivalent guided interactive flow) for AgentV setup.
• Integrate with plugin-manager-first install path:
  • npx allagents plugin marketplace add EntityProcess/agentv
  • npx allagents plugin install agentv-dev@agentv
• Ensure onboarding can:
  • detect/install AgentV CLI when missing
  • initialize bootstrap files (.env.example, .agentv/config.yaml, .agentv/targets.yaml)
  • verify setup and report next steps
• Align docs with the new interactive flow once implemented.

Acceptance Signals

• New users can complete setup from an interactive agent-driven onboarding path without needing to know agentv init first.
• Onboarding handles missing CLI and verification failures with actionable remediation.
• Flow is compatible with allagents/Claude/Copilot command surfaces.
• Documentation reflects the interactive onboarding as canonical.

Non-Goals

• Evaluator/runtime behavior changes in packages/core.
• New evaluator primitives.

Related

• feat(plugin): onboarding skill + docs in one PR #393
• PR feat(plugin): onboarding skill + idempotent bootstrap flow #396