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

docs/design/INDEX.md

@@ -1318,6 +1318,15 @@ the one-method `MemberRunner` seam, so consumers (the `aura` CLI today; the play
 tests tomorrow) bind their own runners while the semantics live here once. It is
 explicitly NOT C21's World (a project-side program): it realizes one campaign document
 and owns no topology, no data sources, no UI.
+**Realization (2026-07-12 — wiring-only tier, #241).** The smallest project
+is now data-only: `Aura.toml` + `blueprints/` + `runs/`, no crate. The load
+boundary tier-selects (a `[nodes]` pointer list in `Aura.toml` → load that
+crate; a root `Cargo.toml` → the pre-#241 native project, unchanged; neither
+→ std-vocabulary-only). `aura new` scaffolds the data-only tier;
+`aura nodes new` scaffolds a node crate **beside** the project and attaches
+it — the visible role-2 switch (C25 role model). Provenance widened
+additively: a data-only run stamps commit-only. Invariant 9's "a project is
+always a Rust crate" was deliberately amended (user decision, 2026-07-12).
 
 ### C17 — Authoring surface
 **Guarantee.** All *logic* — nodes, strategies, **and experiments/harnesses** —