chore: scaffold Aura workspace skeleton (Stage 0)

- 6-crate Cargo workspace, dependency tree frozen (cargo check green in ~1m)
- ml-kem 0.3 (FIPS 203) replaces spec's pqcrypto-kyber for ML-KEM-768
- fix invalid target-gated workspace.dependencies: Windows deps (wintun/windows)
  declared untargeted, cfg-gated per-crate in aura-tunnel
- version bumps vs spec: tun 0.8, rcgen 0.14, wintun 0.5
- stub lib/main per crate; real implementations land wave by wave

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/aura-cli/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "aura-cli"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+description = "Aura CLI: client/server binary, PKI management, split-tunnel admin"
+
+[[bin]]
+name = "aura"
+path = "src/main.rs"
+
+[dependencies]
+aura-crypto.workspace = true
+aura-pki.workspace = true
+aura-proto.workspace = true
+aura-transport.workspace = true
+aura-tunnel.workspace = true
+clap.workspace = true
+tokio.workspace = true
+toml.workspace = true
+serde.workspace = true
+tracing.workspace = true
+tracing-subscriber.workspace = true
+anyhow.workspace = true
+uuid.workspace = true

crates/aura-cli/src/main.rs

@@ -0,0 +1,5 @@
+//! aura — client/server binary and PKI/admin CLI (skeleton; implemented in Wave 4).
+
+fn main() {
+    println!("aura: skeleton binary (implemented in Wave 4)");
+}