docs: two-tier project model — layout, guide, glossary, ledger, invariant 9 (#241 T7)

- CLAUDE.md invariant 9 amended end to end: a project is a directory
  anchored by a static Aura.toml, data-only by default; native node
  logic lives in attached node crates (the nodes/ antecedent removed —
  user decision 2026-07-12, re-opened by the role model's diagnosis).
- docs/project-layout.md reworked to the two tiers (data-only default
  tree + sibling node crate, workspace note under the crate half); the
  day-in-the-life walkthrough now attaches the project's node crate
  once and wires the namespace the shown command actually produces.
- docs/authoring-guide.md: data-only quickstart (closed run target,
  open sweep target) + `aura nodes new` as the native entry; section
  cross-reference updated.
- docs/glossary.md: new "data-only project" and "node crate" entries;
  Aura.toml and manifest entries carry the tier split.
- docs/design/INDEX.md: realization note (wiring-only tier, #241) in
  the project-environment section.
- rustdoc: `[nodes]` intra-doc-link escapes in project.rs/main.rs.

Full gates green: workspace suite (all binaries), clippy -D warnings,
doc build without new warnings.

closes #241

CLAUDE.md

@@ -107,14 +107,19 @@ design decision, not a refactor, and belongs in the ledger.
    never hot-swapped (audit trail: this bot = this commit).
 9. **Engine / project separation.** This repo is the reusable *engine*. Research
    projects are separate external repos that depend on it. Project-specific
-   signals live in a project's `nodes/`; cross-project-reusable nodes in shared
-   crates; universal blocks in `aura-std` (shipped here). Reuse is cargo-native;
-   the hot-reload unit is always the project-side `cdylib`. No user/project
+   *native* nodes live in the project's attached node crate;
+   cross-project-reusable nodes in shared crates; universal blocks in
+   `aura-std` (shipped here). Reuse is cargo-native. No user/project
    signals in this repo (only `examples/` fixtures for the engine's own tests);
-   no multi-project manager or node registry inside aura. **A project is always
-   a Rust crate** (a cdylib library of node / strategy / experiment blueprints +
-   a static `Aura.toml`), hosted by `aura` during research and frozen to a
-   standalone binary for deploy.
+   no multi-project manager or node registry inside aura. **A project is a
+   directory anchored by a static `Aura.toml`** — data-only by default
+   (blueprints + research documents over the std vocabulary, no build step),
+   hosted by `aura` during research and frozen to a standalone binary for
+   deploy. Native node logic lives in **node crates**: separate cdylib crates
+   referenced via `Aura.toml [nodes]`, scaffolded/attached by a dedicated verb
+   (the visible role-2 switch); the hot-reload unit is the referenced
+   node-crate cdylib. (#241 amendment, 2026-07-12 — re-opened deliberately by
+   the role model's diagnosis.)
 10. **Authoring surface — all logic is Rust.** Node, strategy, and harness
     *logic* is authored in native Rust via Claude Code + the skills pipeline,
     using builder APIs. Declarative config (`Aura.toml`) carries only static