- Move runCtx/runCancel creation before event handler registration and
QR loop so Stop() can cancel at any point during startup
- Replace blocking QR event loop in Start() with a background goroutine
that selects on runCtx.Done(), preventing Start() from hanging
indefinitely when waiting for QR scan
- Track all background goroutines (QR handler, reconnect) with
sync.WaitGroup; Stop() waits for them to finish before releasing
client/container resources
- Cancel runCtx on error paths in Start() to avoid leaked contexts
Fixes resource leak introduced in #655.
