docs: add agent-handoff playbook (portable analysis methodology)

[Dav1108]

What

Adds handoff.md — a portable, self-driving methodology playbook that lets another agent reproduce the Hackagotchi product-strategy analysis for other GhostLabs projects (Kestrel, PicoInky, …).

Contents

• Operating principles — adversarial verification, honest ceilings, lead-with-the-wedge, decisive calls, can-vs-should.
• Phase 0 — understand the target project and adapt (project-type table: hardware / SaaS / dev-tool / service → which phases apply).
• The phases — A (go-to-market), B (virality/adoption), C (monetization/pricing/manufacturing), plus cross-cutting licensing + tangible-asset spec, each as fan-out lenses → adversarial critic → synthesis.
• Reusable templates — lens/critic output schemas + generic lens & critic prompts.
• Hard-won defaults from the Hackagotchi run.
• Pre-authorized delivery flow — commit → push → open PR → sync with main.

Notes

• Docs only — no code or behavior changes.
• References the merged Hackagotchi analysis (docs/, the GPL-3.0 relicense, the enclosure spec) as the worked example.

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