fix: HackRF One support — detection, ADS-B, waterfall, and error handling

- Parse hackrf_info stderr (newer firmware) and handle non-zero exit codes
- Fix gain_max from 62 to 102 (combined LNA 40 + VGA 62)
- Apply resolved readsb binary path for all SDR types, not just RTL-SDR
- Add HackRF/SoapySDR-specific error messages in ADS-B startup
- Add HackRF waterfall support via rx_sdr IQ capture + FFT
- Add 17 tests for HackRF detection and command builder

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_hackrf_commands.py

@@ -0,0 +1,88 @@
+"""Tests for HackRF command builder."""
+
+from utils.sdr.base import SDRDevice, SDRType
+from utils.sdr.hackrf import HackRFCommandBuilder
+
+
+def _make_device(serial: str = 'abc123') -> SDRDevice:
+    return SDRDevice(
+        sdr_type=SDRType.HACKRF,
+        index=0,
+        name='HackRF One',
+        serial=serial,
+        driver='hackrf',
+        capabilities=HackRFCommandBuilder.CAPABILITIES,
+    )
+
+
+class TestHackRFCapabilities:
+    def test_gain_max_reflects_combined_lna_vga(self):
+        """gain_max should be LNA(40) + VGA(62) = 102."""
+        assert HackRFCommandBuilder.CAPABILITIES.gain_max == 102.0
+
+    def test_frequency_range(self):
+        caps = HackRFCommandBuilder.CAPABILITIES
+        assert caps.freq_min_mhz == 1.0
+        assert caps.freq_max_mhz == 6000.0
+
+    def test_tx_capable(self):
+        assert HackRFCommandBuilder.CAPABILITIES.tx_capable is True
+
+
+class TestSplitGain:
+    def test_low_gain_all_to_lna(self):
+        builder = HackRFCommandBuilder()
+        lna, vga = builder._split_gain(30)
+        assert lna == 30
+        assert vga == 0
+
+    def test_gain_at_lna_max(self):
+        builder = HackRFCommandBuilder()
+        lna, vga = builder._split_gain(40)
+        assert lna == 40
+        assert vga == 0
+
+    def test_high_gain_splits_across_stages(self):
+        builder = HackRFCommandBuilder()
+        lna, vga = builder._split_gain(80)
+        assert lna == 40
+        assert vga == 40
+
+    def test_max_combined_gain(self):
+        builder = HackRFCommandBuilder()
+        lna, vga = builder._split_gain(102)
+        assert lna == 40
+        assert vga == 62
+
+
+class TestBuildAdsbCommand:
+    def test_contains_soapysdr_device_type(self):
+        builder = HackRFCommandBuilder()
+        cmd = builder.build_adsb_command(_make_device(), gain=40)
+        assert '--device-type' in cmd
+        assert 'soapysdr' in cmd
+
+    def test_includes_serial_in_device_string(self):
+        builder = HackRFCommandBuilder()
+        cmd = builder.build_adsb_command(_make_device(serial='deadbeef'), gain=40)
+        device_idx = cmd.index('--device')
+        assert 'deadbeef' in cmd[device_idx + 1]
+
+
+class TestBuildIQCaptureCommand:
+    def test_outputs_cu8_to_stdout(self):
+        builder = HackRFCommandBuilder()
+        cmd = builder.build_iq_capture_command(
+            _make_device(), frequency_mhz=100.0, sample_rate=2048000, gain=40
+        )
+        assert '-F' in cmd
+        assert 'CU8' in cmd
+        assert cmd[-1] == '-'
+
+    def test_gain_split_in_command(self):
+        builder = HackRFCommandBuilder()
+        cmd = builder.build_iq_capture_command(
+            _make_device(), frequency_mhz=100.0, gain=80
+        )
+        gain_idx = cmd.index('-g')
+        assert cmd[gain_idx + 1] == 'LNA=40,VGA=40'