feat: APRS export, USRP support, and MQTT data export (closes #222)

- GET /aprs/export?format=json|csv downloads all tracked APRS stations
- USRP (Ettus N200/B200/B210) detected via SoapyUHD and supported across
  all signal modes (FM demod, ADS-B, ISM, AIS, I/Q capture)
- Optional MQTT publisher broadcasts decoded events from every module;
  enabled by setting INTERCEPT_MQTT_BROKER, disabled by default
- paho-mqtt added to requirements.txt (optional dep)
- .gitignore: add *.kismet, aircraft_db.json/meta, SoapySDR/
- Bump version to 2.30.0

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

utils/sdr/usrp.py

@@ -0,0 +1,153 @@
+"""
+USRP command builder implementation.
+
+Uses SoapySDR (via the UHD driver / SoapyUHD bridge) for all signal
+processing tasks.  The same rx_fm / rx_sdr / rtl_433 / AIS-catcher
+toolchain used by HackRF applies here because they all speak SoapySDR.
+
+Tested target: USRP N200 / B200 / B210 (UHD driver, SoapyUHD bridge).
+Requires: uhd, SoapySDR, SoapyUHD installed on the host or in Docker.
+"""
+
+from __future__ import annotations
+
+from utils.dependencies import get_tool_path
+
+from .base import CommandBuilder, SDRCapabilities, SDRDevice, SDRType
+
+
+class USRPCommandBuilder(CommandBuilder):
+    """USRP command builder using SoapySDR / UHD."""
+
+    CAPABILITIES = SDRCapabilities(
+        sdr_type=SDRType.USRP,
+        freq_min_mhz=1.0,
+        freq_max_mhz=6000.0,
+        gain_min=0.0,
+        gain_max=76.0,  # typical UHD normalised gain range
+        sample_rates=[1000000, 2000000, 4000000, 8000000, 16000000, 25000000],
+        supports_bias_t=False,
+        supports_ppm=False,
+        tx_capable=True,
+        supports_iq_capture=True,
+    )
+
+    def _build_device_string(self, device: SDRDevice) -> str:
+        """Build SoapySDR device string for USRP."""
+        if device.serial and device.serial not in ("N/A", "Unknown"):
+            return f"driver=uhd,serial={device.serial}"
+        return "driver=uhd"
+
+    def build_fm_demod_command(
+        self,
+        device: SDRDevice,
+        frequency_mhz: float,
+        sample_rate: int = 22050,
+        gain: float | None = None,
+        ppm: int | None = None,
+        modulation: str = "fm",
+        squelch: int | None = None,
+        bias_t: bool = False,
+    ) -> list[str]:
+        device_str = self._build_device_string(device)
+        rx_fm_path = get_tool_path("rx_fm") or "rx_fm"
+        cmd = [
+            rx_fm_path,
+            "-d",
+            device_str,
+            "-f",
+            f"{frequency_mhz}M",
+            "-M",
+            modulation,
+            "-s",
+            str(sample_rate),
+        ]
+        if gain is not None and gain > 0:
+            cmd.extend(["-g", str(int(gain))])
+        if squelch is not None and squelch > 0:
+            cmd.extend(["-l", str(squelch)])
+        cmd.append("-")
+        return cmd
+
+    def build_adsb_command(self, device: SDRDevice, gain: float | None = None, bias_t: bool = False) -> list[str]:
+        device_str = self._build_device_string(device)
+        cmd = ["readsb", "--net", "--device-type", "soapysdr", "--device", device_str, "--quiet"]
+        if gain is not None:
+            cmd.extend(["--gain", str(int(gain))])
+        return cmd
+
+    def build_ism_command(
+        self,
+        device: SDRDevice,
+        frequency_mhz: float = 433.92,
+        gain: float | None = None,
+        ppm: int | None = None,
+        bias_t: bool = False,
+    ) -> list[str]:
+        device_str = self._build_device_string(device)
+        cmd = ["rtl_433", "-d", device_str, "-f", f"{frequency_mhz}M", "-F", "json"]
+        if gain is not None and gain > 0:
+            cmd.extend(["-g", str(int(gain))])
+        return cmd
+
+    def build_ais_command(
+        self,
+        device: SDRDevice,
+        gain: float | None = None,
+        bias_t: bool = False,
+        tcp_port: int = 10110,
+        udp_host: str | None = None,
+        udp_port: int | None = None,
+    ) -> list[str]:
+        device_str = self._build_device_string(device)
+        cmd = [
+            "AIS-catcher",
+            "-d",
+            f"soapysdr -d {device_str}",
+            "-S",
+            str(tcp_port),
+            "-o",
+            "5",
+            "-q",
+        ]
+        if gain is not None and gain > 0:
+            cmd.extend(["-gr", "tuner", str(int(gain))])
+        if udp_host and udp_port:
+            cmd.extend(["-u", udp_host, str(udp_port)])
+        return cmd
+
+    def build_iq_capture_command(
+        self,
+        device: SDRDevice,
+        frequency_mhz: float,
+        sample_rate: int = 2048000,
+        gain: float | None = None,
+        ppm: int | None = None,
+        bias_t: bool = False,
+        output_format: str = "cu8",
+    ) -> list[str]:
+        device_str = self._build_device_string(device)
+        freq_hz = int(frequency_mhz * 1e6)
+        rx_sdr_path = get_tool_path("rx_sdr") or "rx_sdr"
+        cmd = [
+            rx_sdr_path,
+            "-d",
+            device_str,
+            "-f",
+            str(freq_hz),
+            "-s",
+            str(sample_rate),
+            "-F",
+            "CU8",
+        ]
+        if gain is not None and gain > 0:
+            cmd.extend(["-g", str(int(gain))])
+        cmd.append("-")
+        return cmd
+
+    def get_capabilities(self) -> SDRCapabilities:
+        return self.CAPABILITIES
+
+    @classmethod
+    def get_sdr_type(cls) -> SDRType:
+        return SDRType.USRP