- test_resize_tty: use SyncBox (via runtime.create) instead of
  SyncSimpleBox which lacks tty support
- test_options: fix cmd test to use long-running process, collect
  stdout from execution stream instead of non-existent result.stdout,
  un-skip auto_remove+detach combination test (now accepted by API)
- test_shutdown: rewrite to reuse shared runtime's event loop/dispatcher
  with isolated Boxlite instance to avoid asyncio loop conflicts
- Delete duplicate async test files (test_codebox.py, test_simplebox.py)
  and convert remaining to sync API

Result: 110 passed, 21 skipped (credential-gated), 0 failures.