fix(lefthook): serialize pre-push commands to avoid stdin deadlock

Default parallel execution of sync-check and git-lfs commands within
the pre-push hook deadlocks: both read from stdin (git pipes the push
refspec to pre-push hooks), and two parallel readers never reach EOF.

Add piped: true to force sequential execution. sync-check runs first
(only inspects push_files via lefthook templating, doesn't actually
consume stdin), then git-lfs runs second with clean stdin access.

Observed during chore/test-infra-001 sprint: LFS upload completed
100% but pre-push hook hung indefinitely. Workaround was --no-verify;
this commit removes the need for that.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

lefthook.yml

@@ -17,6 +17,10 @@ post-commit:
       run: bash .githooks/post-commit
 
 pre-push:
+  # piped: true forces serial execution. Both sync-check and git-lfs
+  # read from stdin (git pipes the push refspec to pre-push hooks);
+  # default parallel execution deadlocks with two stdin readers.
+  piped: true
   commands:
     sync-check:
       run: bash .githooks/pre-push