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

crates/aura-cli/src/main.rs

@@ -2489,7 +2489,7 @@ struct NodesCmd {
 
 #[derive(Subcommand)]
 enum NodesCommand {
-    /// Scaffold a node crate beside this project and attach it via [nodes].
+    /// Scaffold a node crate beside this project and attach it via `[nodes]`.
     New(NodesNewCmd),
 }
 

crates/aura-cli/src/project.rs

@@ -475,8 +475,8 @@ fn newest_source_mtime(root: &Path) -> Option<SystemTime> {
     newest
 }
 
-/// Discover the project's tier and load it. Data-only (no [nodes], no root
-/// crate) loads nothing; a [nodes] pointer or a root Cargo.toml routes into
+/// Discover the project's tier and load it. Data-only (no `[nodes]`, no root
+/// crate) loads nothing; a `[nodes]` pointer or a root Cargo.toml routes into
 /// the unchanged crate pipeline (`load_crate`).
 pub fn load(root: &Path, release: bool) -> Result<ProjectEnv, ProjectError> {
     let toml = parse_aura_toml(root)?;