fix(#2560): kill_on_drop for git + nix children so timeouts don't orphan

hive-c0re/src/lifecycle/git.rs

@@ -47,10 +47,17 @@ pub(super) async fn git_commit(dir: &Path, message: &str) -> Result<()> {
 
 /// Spawn `git` honoring the `HYPERHIVE_GIT` env var (absolute path baked in
 /// by the NixOS module), falling back to bare `git` (PATH lookup) otherwise.
+///
+/// `kill_on_drop(true)`: if the caller's future is dropped before the child
+/// exits — e.g. a `tokio::time::timeout` around startup migration fires — the
+/// git child is killed instead of orphaned (left retrying an unreachable
+/// forge). No-op on normal completion, where the child has already exited.
 #[must_use]
 pub fn git_command() -> Command {
     let exe = std::env::var("HYPERHIVE_GIT").unwrap_or_else(|_| "git".into());
-    Command::new(exe)
+    let mut cmd = Command::new(exe);
+    cmd.kill_on_drop(true);
+    cmd
 }
 
 pub async fn git(dir: &Path, args: &[&str]) -> Result<()> {