refactor(portal): move command runner into module

adk-rust/crates/detmir-portal/src/command_runner.rs

@@ -0,0 +1,26 @@
+//! External command execution helpers for the portal.
+//!
+//! CONTRACT: these helpers are intentionally small and side-effect explicit.
+//! They preserve stdout/stderr error text because readiness verification APIs
+//! expose command failure diagnostics to operators.
+
+use std::path::Path;
+use std::process::Command;
+
+pub(crate) fn run_in_dir(dir: &Path, command: &mut Command) -> std::result::Result<(), String> {
+    let output = command
+        .current_dir(dir)
+        .output()
+        .map_err(|err| format!("run command in {}: {err}", dir.display()))?;
+    if output.status.success() {
+        Ok(())
+    } else {
+        Err(format!(
+            "{}{}",
+            String::from_utf8_lossy(&output.stdout),
+            String::from_utf8_lossy(&output.stderr)
+        )
+        .trim()
+        .to_string())
+    }
+}