feat(cli): print the engine commit in --version

aura --version now prints 'aura 0.1.0 (<commit>)', the commit sourced
from the same AURA_COMMIT build provenance the run manifest stamps
(option_env! at build time, 'unknown' fallback, dirty suffix included)
— a pre-run freshness probe: a stale binary is now distinguishable from
an engine bug at the CLI surface, and research docs pinning
'Engine: aura @ <sha>' can verify the binary they invoke.

The version string is memoized as a OnceLock-leaked &'static str:
clap 4.6's builder Str accepts only &'static str (no From<String>), so
the owned-String alternative a quality pass suggested does not build —
verified, held with evidence in the loop report.

closes #266

crates/aura-cli/src/main.rs

@@ -125,7 +125,7 @@ fn sim_optimal_manifest(
     // Typed params pass straight through: the manifest carries self-describing
     // Scalars, so a length stays `i64` and a scale `f64` in the record.
     RunManifest {
-        commit: option_env!("AURA_COMMIT").unwrap_or("unknown").to_string(),
+        commit: ENGINE_COMMIT.to_string(),
         params,
         defaults: Vec::new(),
         window,
@@ -2640,10 +2640,36 @@ fn parse_scalar_csv(csv: &str) -> Option<Vec<Scalar>> {
 // the campaign path. Usage errors (clap parse + argv-applicability guards) exit 2;
 // runtime failures exit 1.
 
-/// The `aura` root parser. `#[command(version)]` reads `CARGO_PKG_VERSION`
+/// The single build-time commit provenance (`option_env!("AURA_COMMIT")`,
-/// (the workspace `0.1.0`), so `aura --version` prints `aura 0.1.0`.
+/// falling back to `"unknown"`): both `--version` (via `version_string`) and
+/// `sim_optimal_manifest`'s `RunManifest.commit` read this one const, so a
+/// stale binary is distinguishable from a fresh one at the CLI surface,
+/// before any run, without a second commit-sourcing mechanism (#266).
+const ENGINE_COMMIT: &str = match option_env!("AURA_COMMIT") {
+    Some(c) => c,
+    None => "unknown",
+};
+
+/// `aura 0.1.0 (<commit>)` as a process-lifetime `&'static str` — computed once
+/// (clap's `version` builder method wants `Into<Str>`, and `clap::builder::Str`
+/// (clap 4.6) only implements `From<&'static str>`, not `From<String>`, so the
+/// one owned `String` this formats is leaked for the process's lifetime, same
+/// as any other CLI one-shot startup string).
+fn version_string() -> &'static str {
+    static VERSION: std::sync::OnceLock<String> = std::sync::OnceLock::new();
+    VERSION.get_or_init(|| format!("{} ({ENGINE_COMMIT})", env!("CARGO_PKG_VERSION")))
+}
+
+/// The `aura` root parser. `version` is built from `CARGO_PKG_VERSION` (the
+/// workspace `0.1.0`) plus the parenthesized `ENGINE_COMMIT`, so
+/// `aura --version` prints `aura 0.1.0 (<commit>)`.
 #[derive(Parser)]
-#[command(name = "aura", version, about = "Author, backtest, and validate trading strategies — research CLI", infer_long_args = true)]
+#[command(
+    name = "aura",
+    version = version_string(),
+    about = "Author, backtest, and validate trading strategies — research CLI",
+    infer_long_args = true
+)]
 struct Cli {
     #[command(subcommand)]
     command: Command,