chore: scaffold aura workspace and wire the skills dev-cycle

Cargo workspace aura-core -> aura-engine -> aura-cli (bin `aura`) plus nodes/ for hot-reloadable cdylib node crates. Crate bodies are intentionally API-free; types arrive from the first spec. Adds the skills profile (.claude/dev-cycle-profile.yml), the project CLAUDE.md with the eight domain invariants, and the design-ledger skeleton.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/aura-core/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "aura-core"
+edition.workspace = true
+version.workspace = true
+license.workspace = true
+publish.workspace = true
+
+[dependencies]

crates/aura-core/src/lib.rs

@@ -0,0 +1,17 @@
+//! `aura-core` — the shared contract every aura component links against.
+//!
+//! This crate is the boundary forced by the cdylib hot-reload model: both the
+//! engine and every hot-reloadable node cdylib depend on it, so it must stay
+//! small and stable. It is the home of (to be specified):
+//!
+//! - the scalar base types streamed as SoA: `i64`, `f64`, `bool`, `timestamp`;
+//! - the `Node` trait — the contract an authored node implements (`schema` +
+//!   `eval`), with engine-provided read-only input windows and node-internal
+//!   series;
+//! - the evaluation context `Ctx` (zero-copy indexed access into input columns,
+//!   fresh-mask, current-cycle timestamp);
+//! - the firing-policy declarations (A: fire-on-any-fresh + hold; B: all-fresh
+//!   barrier), declarable per input group.
+//!
+//! Types are intentionally absent until the first spec lands under
+//! `docs/specs/`. This crate documents intent; it does not yet define API.