Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/tools/country-data/plot.py

@@ -0,0 +1,68 @@
+#!/usr/bin/env python3
+# /// script
+# requires-python = ">=3.9"
+# dependencies = ["matplotlib", "shapely"]
+# ///
+"""Plot country polygons from a Vanetza country data binary file."""
+import argparse
+import colorsys
+import struct
+import sys
+
+import matplotlib.pyplot as plt
+from shapely import wkb
+
+EXPECTED_FORMAT_VERSION = 1
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Plot country polygons from .bin file")
+    parser.add_argument("input", help="Path to country_data.bin")
+    args = parser.parse_args()
+
+    fig, ax = plt.subplots(figsize=(16, 8))
+
+    with open(args.input, "rb") as f:
+        data = f.read()
+
+    if len(data) < 2:
+        print("Error: file too short to contain version header", file=sys.stderr)
+        sys.exit(1)
+
+    version, = struct.unpack_from("<H", data, 0)
+    if version != EXPECTED_FORMAT_VERSION:
+        print(f"Error: unsupported country data format version {version}", file=sys.stderr)
+        sys.exit(1)
+
+    offset = 2
+    while offset < len(data):
+        m49, = struct.unpack_from("<H", data, offset)
+        offset += 2
+        wkb_size, = struct.unpack_from("<I", data, offset)
+        offset += 4
+        geom = wkb.loads(data[offset:offset + wkb_size])
+        offset += wkb_size
+
+        h = (m49 * 0.618) % 1.0
+        s = 0.5 + (hash(m49) % 50) / 100.0
+        l = 0.4 + (hash(m49 * 7) % 30) / 100.0
+        color = colorsys.hls_to_rgb(h, l, s)
+
+        for polygon in geom.geoms:
+            x, y = polygon.exterior.xy
+            ax.fill(x, y, alpha=0.4, edgecolor="black", linewidth=0.3, facecolor=color)
+            if polygon.area > 1.0:
+                centroid = polygon.centroid
+                ax.text(centroid.x, centroid.y, str(m49),
+                        fontsize=5, ha="center", va="center")
+
+    ax.set_aspect("equal")
+    ax.set_xlabel("Longitude")
+    ax.set_ylabel("Latitude")
+    ax.set_title("Country Polygons")
+    plt.tight_layout()
+    plt.show()
+
+
+if __name__ == "__main__":
+    main()