Fixes three CI failures identified in workflow run #19395416465:
1. **Missing threading import** (test_peripheral_disconnect_cleanup.py)
- Added missing `import threading` to fix NameError during test setup
- Tests use threading.RLock() but import was missing
2. **Timing race condition** (test_stale_connection_polling.py)
- Increased sleep from 0.15s to 1.5s in test_polling_interval_30_seconds
- Test expects 2 polling cycles at 0.6s each, was timing out in CI
3. **Container-aware Bluetooth checks** (install.sh)
- Added is_container() helper to detect Docker/container environments
- Skip Bluetooth adapter power checks in containers (no hardware access)
- Prevents false failures from bluetoothctl crashes in CI environments
All changes are test/installer infrastructure only - no production code changes.
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Co-Authored-By: Claude <noreply@anthropic.com>
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