docs: design pack index

design/README.md

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+# Design pack (product SSOT)
+
+This folder is the **product design source of truth** for Salon_Assistant / Lumina.
+
+| Document | Purpose |
+|----------|---------|
+| [DESIGN_PLAN.md](DESIGN_PLAN.md) | Architecture + implementation plan (NemoClaw/Hermes, install, MCP, updates) |
+| [use-cases.md](use-cases.md) | Use-case catalog (SSOT — do not duplicate full matrices elsewhere) |
+| [scenarios.md](scenarios.md) | Narrative scenarios for design and future tests |
+| [DECISIONS.md](DECISIONS.md) | Resolved decisions from planning |
+| [planes.md](planes.md) | Capability planes |
+| [det-vs-inf.md](det-vs-inf.md) | Deterministic code vs model inference |
+| [mcp-integrations.md](mcp-integrations.md) | Square / QBO / Vagaro / channels |
+| [updates-lifecycle.md](updates-lifecycle.md) | Software update model and vectors |
+
+Operator runbooks live under [`../docs/`](../docs/) and **link here** for design rationale.
+
+**Implementation** of code under `skills/`, `scripts/`, etc. requires an explicit **build** / **implement** order.