docs(vibe): bootstrap vibe/ knowledge tree + ecosystem AGENTS.md

Add a root AGENTS.md (ecosystem map of factory/tools/cms + agent operating
rules + the persona cohort & workflow) and a new vibe/ knowledge base for LLM
agents, modeled on tree-docs conventions and the factory house style.

vibe/ folders (each with a README hub + contribution rules):
- ADR/      optimized MADR-lite; canonical home going forward (doc/adr stays historical)
- PRD/      one subfolder per PRD, mandatory STATUS.md, QA strategy for big ones
- investigations/  single INV-NNN-slug.md, or stub + folder w/ notebooks
- guidebooks/      tree-docs maps; lab-ecosystem guidebook of factory+tools+cms
- runbooks/        [AGENT]/[HUMAN] step procedures (EN; doc/runbooks stays FR)
- shareouts/       dated FR handouts (decks/mp4)

Seed content (first ADR + PRD): a safe, production-like environment to rehearse
risky changes and recovery without touching real prod — local-only sandbox
(k3d + arm64 VMs) with a hard prod/sandbox isolation boundary. Includes
INV-001 (prod blast-radius couplings), the ecosystem guidebook, and a FR shareout.

Conventions enforced: no-tombstone rule, breadcrumb spine, bidirectional
cross-links, theme:base mermaid (MCP-validated) + ordered-list-after-diagram.
Built with a Workflow + persona cohort; 24 files, zero dead links.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

vibe/PRD/README.md

@@ -0,0 +1,34 @@
+[vibe](../README.md) > **PRD**
+
+# Product Requirement Documents
+
+> **Status**: 🟢 Active
+> **Last Updated**: 2026-06-23
+> **Related**: [vibe/ADR](../ADR/README.md) · [vibe/Investigations](../investigations/README.md)
+
+`vibe/PRD/` holds the Product Requirement Documents that drive larger pieces of work in the lab. A PRD captures *what* we want and *why it matters*; the matching ADRs capture *how we decided to build it*, and investigations capture *what we learned* along the way.
+
+## Convention
+
+- **One subfolder per PRD**, kebab-case (e.g. `safe-prod-like-environment/`).
+- Each subfolder **MUST** contain:
+  - `README.md` — the PRD hub: problem, goals/non-goals, requirements, success criteria, and a QA strategy.
+  - `STATUS.md` — the implementation tracker. **Update it whenever something ships** (a PR merges, a brick lands, a milestone closes). It is the living view of "where are we" against the PRD.
+- A **big PRD uses tree-docs**: the `README.md` stays a hub and detail lives in leaf pages (each with its own breadcrumb and bidirectional cross-links). A tree-sized PRD **MUST** detail an explicit **QA strategy** — how the delivered work will be verified, and what "done and safe" means.
+- **PRs cross-link to the PRD**, and the PRD's `STATUS.md` **cross-links back** to the PRs/ADRs/investigations that realised each part. Links are bidirectional.
+- **No-tombstone rule** applies: the PRD reads as currently true. Progress lives in `STATUS.md` (which *is* a tracker and may legitimately list shipped items), not as "previously / now" edits scattered through the hub.
+
+## Index
+
+| PRD | Hub | Status |
+| --- | --- | --- |
+| Safe, production-like environment | [safe-prod-like-environment/README.md](safe-prod-like-environment/README.md) | 🟡 In design |
+
+## Rules to contribute
+
+1. Create a kebab-case subfolder named for the PRD.
+2. Add `README.md` (the hub) and `STATUS.md` (the tracker). Both carry a breadcrumb first line and the leaf header blockquote (Status / Last Updated / Related).
+3. In the hub, state the problem, goals and non-goals, requirements, success criteria, and the QA strategy. If the PRD is large, split detail into leaf pages and keep the README as a navigable hub.
+4. Keep `STATUS.md` current: every time a piece ships, record it there and link the PR/ADR that delivered it.
+5. Add a row to the Index table above.
+6. Ensure every PR that implements part of the PRD links to the PRD, and that `STATUS.md` links back. Bidirectional links are mandatory.