The #getGitStatus() method fires an async `git status --porcelain` but
only updates the TTL timestamp after the async completes. In large repos
where git status takes seconds, every TUI render cycle during that window
spawns a new process — cascading into hundreds of concurrent git processes,
exhausting file descriptors and creating .git/index.lock contention.
Add a #gitStatusInFlight boolean guard that ensures exactly one git status
process runs at a time. Use a finally block to unconditionally reset the
guard and refresh the TTL to completion time.
