feat(drone): add RFDetector for rtl_433 and hackrf_sweep control-link detection

Implements RFDetector class that wraps rtl_433 (433/868MHz) and hackrf_sweep
(2.4/5.8GHz) subprocesses, emitting RFObservation objects onto a shared queue.
Includes signature matching, frequency band validation, and power thresholding.

- _handle_rtl433_line(): Parse JSON output, filter drone bands, emit observations
- _handle_hackrf_line(): Parse CSV output, average power levels, threshold at -90dBm
- start()/stop(): Manage subprocess threads for concurrent RF detection
- Graceful handling of missing tools (rtl_433, hackrf_sweep)

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

tests/test_drone_rf_detector.py

@@ -0,0 +1,83 @@
+"""Tests for RFDetector (rtl_433 + hackrf_sweep control-link detection)."""
+
+from __future__ import annotations
+
+import json
+import queue
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from utils.drone.models import RFObservation
+from utils.drone.rf_detector import RFDetector
+
+
+@pytest.fixture
+def detector():
+    q = queue.Queue()
+    return RFDetector(output_queue=q), q
+
+
+def test_detector_not_running_initially(detector):
+    det, q = detector
+    assert not det.running
+
+
+def test_rtl433_json_line_emits_observation(detector):
+    det, q = detector
+    rtl433_line = json.dumps(
+        {
+            "freq": 433920000,
+            "rssi": -68.5,
+            "protocol": "FrSky",
+        }
+    )
+    det._handle_rtl433_line(rtl433_line)
+    obs = q.get_nowait()
+    assert isinstance(obs, RFObservation)
+    assert obs.frequency_hz == 433_920_000
+    assert obs.hardware == "RTL433"
+    assert obs.rssi == -68.5
+
+
+def test_rtl433_non_json_line_ignored(detector):
+    det, q = detector
+    det._handle_rtl433_line("not json at all")
+    assert q.empty()
+
+
+def test_hackrf_sweep_line_emits_observation(detector):
+    det, q = detector
+    # hackrf_sweep CSV: date, time, hz_low, hz_high, hz_bin_width, num_samples, db, db, ...
+    hz_low = 2_440_000_000
+    hz_high = 2_441_000_000
+    sweep_line = f"2026-05-03, 12:00:00, {hz_low}, {hz_high}, 1000000, 10, -45.2, -46.1, -44.8"
+    det._handle_hackrf_line(sweep_line)
+    obs = q.get_nowait()
+    assert isinstance(obs, RFObservation)
+    assert obs.hardware == "HACKRF"
+    assert obs.frequency_hz == hz_low
+    assert obs.rssi < 0
+
+
+def test_hackrf_sweep_below_threshold_ignored(detector):
+    det, q = detector
+    hz_low = 2_440_000_000
+    hz_high = 2_441_000_000
+    # Very low power — should be ignored (below -90 dBm threshold)
+    sweep_line = f"2026-05-03, 12:00:00, {hz_low}, {hz_high}, 1000000, 10, -95.0, -96.0, -95.5"
+    det._handle_hackrf_line(sweep_line)
+    assert q.empty()
+
+
+def test_start_stop(detector):
+    det, q = detector
+    mock_proc = MagicMock()
+    mock_proc.stdout = MagicMock()
+    mock_proc.stdout.readline = MagicMock(side_effect=[b""])
+    with patch("subprocess.Popen", return_value=mock_proc):
+        with patch("shutil.which", return_value="/usr/bin/rtl_433"):
+            det.start(rtl_sdr_index=0)
+    assert det.running
+    det.stop()
+    assert not det.running