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-cli/src/main.rs

@@ -0,0 +1,8 @@
+//! `aura` — the programmatic / CLI face of the engine (the surface the LLM and
+//! automation drive: author a node, run a sim/sweep, emit structured metrics).
+//!
+//! Skeleton only: real subcommands arrive with the walking-skeleton milestone.
+
+fn main() {
+    println!("aura: walking-skeleton scaffold — no subcommands yet.");
+}