Replace polling waitForProcess with Process.terminationHandler bridge

[poolcamacho]

Context

GitService.waitForProcess(_:timeout:) currently polls process.isRunning in a loop with Thread.sleep(0.05) on a global concurrent queue. That burns a CPU slot and ties up a worker thread for the entire duration of every git command (which adds up: every refresh fans out to status, log, branches, currentBranch, stash list).

Suggested by feedback on r/swift.

Proposal

Bridge Process.terminationHandler directly into a withCheckedContinuation. Process fires the handler the instant the child exits, so no polling is needed. Race it against a Task.sleep-based timeout that calls process.terminate() and resumes with false.

Sketch:

func waitForProcess(_ process: Process, timeout: TimeInterval) async -> Bool {
    await withCheckedContinuation { continuation in
        let lock = NSLock()
        var resumed = false
        func resumeOnce(_ value: Bool) {
            lock.lock(); defer { lock.unlock() }
            guard !resumed else { return }
            resumed = true
            continuation.resume(returning: value)
        }

        let timeoutTask = Task {
            try? await Task.sleep(for: .seconds(timeout))
            if process.isRunning { process.terminate() }
            resumeOnce(false)
        }

        process.terminationHandler = { _ in
            timeoutTask.cancel()
            resumeOnce(true)
        }
    }
}

The locking is needed because terminationHandler and the timeout task can race.

Acceptance criteria

• Replace the polling loop in Services/GitService.swift
• All existing tests / build still pass
• Manual smoke test: open a repo, perform a few commits / pushes, observe Activity Monitor no longer shows extra busy threads while git is running