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/README.md

@@ -0,0 +1,50 @@
+# vibe/ — Arcodange Knowledge Base
+
+You-are-here: the **root** of the `vibe/` knowledge tree — the front door for every doc agents write and read.
+Up: [factory](../README.md) / [AGENTS.md](../AGENTS.md)
+
+> **Status:** Active
+> **Last Updated:** 2026-06-23
+
+## What is `vibe/`?
+
+`vibe/` is the knowledge base dedicated to **LLM agents** working on the Arcodange lab. It collects the *why* (ADRs), the *what/when* (PRDs), the *what-we-found* (investigations), the *how-it-fits-together* (guidebooks), the *how-to-do-it* (runbooks), and the *what-we-told-humans* (shareouts). Everything here is written in **English** — the single exception is **shareouts handouts, which are FRENCH**. Operating rules (no-tombstone, mermaid prefs, tree-docs, ADR/PRD/investigation conventions, PR crosslinking, language policy) are defined authoritatively in [AGENTS.md](../AGENTS.md); this page summarizes them and points there.
+
+## Folder map
+
+| Folder | When to use it | Status |
+|---|---|---|
+| [ADR](ADR/README.md) | Recording an architecture **decision** (MADR-lite; body immutable once Accepted). Canonical home going forward. | ⬜ |
+| [PRD](PRD/README.md) | Specifying a **product/project**: Problem → … → QA strategy → `STATUS.md` (mandatory, kept current). | ⬜ |
+| [investigations](investigations/README.md) | Capturing a **finding/analysis** — single `INV-NNN-slug.md`, or stub + notebooks when data-heavy. | ⬜ |
+| [guidebooks](guidebooks/README.md) | Mapping a **component or the ecosystem** as navigable tree-docs (the lab cartography). | ⬜ |
+| [runbooks](runbooks/README.md) | Documenting an **operational procedure** step-by-step with `[AGENT]` / `[HUMAN]` markers. | ⬜ |
+| [shareouts](shareouts/README.md) | Producing **handouts/presentations** for humans (FRENCH). | ⬜ |
+
+Status legend: ✅ done · 🟡 beta · 🔴 critical · ⚠️ known issue · ❌ disabled · ⬜ not started.
+
+## Conventions at a glance
+
+- **No-tombstone rule (foremost)** — write each file as currently true; never leave "previously X, now Y", changelogs, or "updated to …" notes. Git history is the audit trail. Only exception: a forward-looking `> [!CAUTION]` about a live risk.
+- **Breadcrumb spine** — every non-root file starts with a breadcrumb: ancestors as relative links, current page bold-unlinked, separator ` > `. This root has no breadcrumb (it uses the you-are-here + up-link above instead).
+- **README hub per folder** — each folder's `README.md` is an index table of its children (link + one-line summary + status), sorted by importance/sequence.
+- **Bidirectional links** — if A references B as related, B references A. Use descriptive link text (never "here"/"this").
+- **Mermaid prefs** — `theme base`/`forest` init directive; legible `classDef` palette (dark fills + light text); `<br>` not `\n`; leading space before slash-labels; validate with the Mermaid MCP; **a numbered ordered list restating the flow after every diagram**.
+- **GitHub alert legend** — `[!NOTE]` info/forward-looking · `[!TIP]` aside · `[!IMPORTANT]` inherent constraint · `[!WARNING]` degraded-but-working · `[!CAUTION]` data-loss/breaking.
+- **Status emoji legend** — ✅ done · 🟡 beta · 🔴 critical · ⚠️ known issue · ❌ disabled · ⬜ not started.
+- **Language policy** — English throughout `vibe/`; FRENCH only for shareouts handouts.
+
+Authority for all of the above: [AGENTS.md](../AGENTS.md).
+
+## Maintenance policy
+
+- **Adding a page** → also add its row to the parent folder's `README.md` index table.
+- **Keep links bidirectional** → when you link A→B, add B→A.
+- **Stamp `Last Updated:`** at each tree root (this file and every guidebook/big-PRD root) after any structural change.
+- **Never tombstone** → edit content in place; let git carry the history.
+- **Guidebook coupling** → changing a documented component means updating its guidebook page in the same change.
+- **PR crosslinks** → every PR references the ADR/PRD it advances; that ADR's References and the PRD's `STATUS.md` link back.
+
+## Cohort + workflow (recap)
+
+Docs here are produced by a cohort of persona subagents — Lab Cartographer, ADR Scribe, PRD Architect, Runbook Engineer, Investigator, Diagram Smith, Continuity Warden — spawned via the Agent tool or a Workflow. The recommended pipeline for substantial contributions is **Scaffold → Author → Validate → Review → Assemble**. Full descriptions and responsibilities live in [AGENTS.md](../AGENTS.md).