Implement bfebbx: Betaflight blackbox extractor

Cross-platform (macOS + Linux) C++17 CLI that extracts a Betaflight FC's
blackbox log in one command: auto-detect the serial port, read craft_name
over the Betaflight CLI, send `msc` to reboot into USB mass storage, wait
for the volume to mount, copy btfl_all.bbl to
<craft_name>_<YYYYMMDD>_<HHMMSS>.bbl, and eject.

Native throughout (termios serial, getmntinfo/proc-mounts mount detection,
DiskArbitration/umount eject); the only subprocess is the Linux udisksctl
eject fallback. Includes CMake/ctest build, unit tests for the pure logic
(naming, craft_name parsing, mount diff, serial via pty, CLI parsing),
README with a manual hardware integration procedure, and design/plan docs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_cli.cpp

@@ -0,0 +1,73 @@
+#include "../src/cli.h"
+#include <cassert>
+#include <cstdio>
+#include <fstream>
+#include <string>
+#include <unistd.h>  // mkdtemp
+
+int main() {
+    using namespace bfebbx;
+
+    // parseArgs
+    {
+        const char* argv[] = {"bfebbx", "--port", "/dev/ttyACM0",
+                              "--output", "/tmp/out", "--craft-name", "Vroom",
+                              "--timeout", "45", "-v"};
+        Options o = parseArgs(10, const_cast<char**>(argv));
+        assert(o.port == "/dev/ttyACM0");
+        assert(o.output == "/tmp/out");
+        assert(o.craftName == "Vroom");
+        assert(o.timeoutSec == 45);
+        assert(o.verbose);
+    }
+    {
+        const char* argv[] = {"bfebbx"};
+        Options o = parseArgs(1, const_cast<char**>(argv));
+        assert(o.output == ".");
+        assert(o.timeoutSec == 30);
+        assert(!o.verbose);
+    }
+    {
+        const char* argv[] = {"bfebbx", "--bogus"};
+        bool threw = false;
+        try { parseArgs(2, const_cast<char**>(argv)); }
+        catch (const std::exception&) { threw = true; }
+        assert(threw);
+    }
+    {
+        const char* argv[] = {"bfebbx", "--timeout", "45abc"};
+        bool threw = false;
+        try { parseArgs(3, const_cast<char**>(argv)); }
+        catch (const std::exception&) { threw = true; }
+        assert(threw);
+    }
+    {
+        const char* argv[] = {"bfebbx", "--timeout", "-5"};
+        bool threw = false;
+        try { parseArgs(3, const_cast<char**>(argv)); }
+        catch (const std::exception&) { threw = true; }
+        assert(threw);
+    }
+    {
+        const char* argv[] = {"bfebbx", "--timeout", "45"};
+        Options o = parseArgs(3, const_cast<char**>(argv));
+        assert(o.timeoutSec == 45);
+    }
+
+    // scanPorts against a temp directory
+    {
+        char tmpl[] = "/tmp/bfebbxXXXXXX";
+        char* dir = mkdtemp(tmpl);
+        assert(dir != nullptr);
+        std::string d = dir;
+        for (const char* n : {"ttyACM0", "ttyACM1", "ttyS0", "random"}) {
+            std::ofstream(d + "/" + n).put('x');
+        }
+        auto ports = scanPorts(d, "ttyACM");
+        assert(ports.size() == 2);
+        assert(ports[0] == d + "/ttyACM0");
+        assert(ports[1] == d + "/ttyACM1");
+    }
+
+    return 0;
+}