refactor(waitgroup): replace Add/Done goroutines with WaitGroup.Go

[Copilot]

This refactors legacy sync.WaitGroup goroutine launch sites to the modern WaitGroup.Go API. It removes manual waitgroup bookkeeping in eligible paths without changing concurrency semantics.

• Scope

  • Update eligible sync.WaitGroup goroutine launches in modules/ssh and the affected Go test files under modules/templates and tests/integration.

• What changed

  • Replace manual wg.Add(1) + go func() { ...; wg.Done() }() patterns with wg.Go(func() { ... }).
  • Keep existing closure behavior intact at each call site rather than changing surrounding control flow.
  • Leave non-eligible waitgroup usage unchanged.

• Result

  • Less error-prone goroutine coordination.
  • Shorter, more idiomatic concurrency code.
  • Easier future cleanup of remaining waitgroup usages.

• Example

  var wg sync.WaitGroup
  
  wg.Go(func() {
  	doWork()
  })
  
  wg.Wait()