Initial commit: simtrace2-pysniff v0.1.0

Python-based SIMtrace2 sniffer — drop-in replacement for simtrace2-sniff.
Single dependency (pyusb), auto-reconnect, GSMTAP/PCAP output, library API.

Modules:
  protocol.py — SIMtrace2 USB sniffing protocol parser
  device.py   — USB discovery + SniffSession with exponential backoff reconnect
  gsmtap.py   — GSMTAP UDP sender for Wireshark
  pcap.py     — PCAP file writer (LINKTYPE_GSMTAP)
  dump.py     — hex dump formatters + file output
  __main__.py — CLI entry point

Startup script sniff-start.sh handles udev permission checks and shows
install instructions. udev rule uses TAG+=uaccess (systemd-logind ACL).

70-simtrace2-pysniff.rules

@@ -0,0 +1,12 @@
+# udev rules for SIMtrace2 USB sniffing (simtrace2-pysniff)
+#
+# Install:
+#   sudo cp 70-simtrace2-pysniff.rules /etc/udev/rules.d/
+#   sudo udevadm control --reload-rules
+#   sudo udevadm trigger
+
+ACTION!="add", GOTO="pysniff_end"
+SUBSYSTEM!="usb", GOTO="pysniff_end"
+ATTRS{idVendor}=="1d50", ATTRS{idProduct}=="60e3", TAG+="uaccess"
+ATTRS{idVendor}=="1d50", ATTRS{idProduct}=="616e", TAG+="uaccess"
+LABEL="pysniff_end"