Backend changes:
- Add supported_sample_rates field to AudioDevice struct
- Detect common audio sample rates (44.1, 48, 88.2, 96, 176.4, 192, 352.8, 384 kHz)
- Use CPAL's supported_output_configs() to check rate support for hw: devices
Frontend changes:
- Display sample rates as subtitle in DeviceDropdown (e.g., "44.1, 48, 96, 192 kHz")
- Only shown for bit-perfect devices where detection is available
- Search not sensitive to sample rates field (per user request)