chore(appliance): sysctl drop-in for larger UDP buffers (4K/5K host send headroom)

The host warns when its UDP socket-buffer grant is small (Linux caps SO_SNDBUF at
net.core.wmem_max, ~208 KB by default). Validated zero-loss at 5K even at that cap,
but raising it gives send-side headroom for higher bitrates / concurrent sessions.
Referenced from the headless-Steam appliance setup. macOS clients need no tuning.

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

scripts/99-punktfunk-net.conf

@@ -0,0 +1,11 @@
+# Larger UDP socket buffers for clean 4K/5K streaming.
+#
+# A single high-resolution frame is a burst (a 5120×1440 keyframe is ~130 packets sent at once),
+# which overflows the Linux default (~208 KB) — dropping packets and, under infinite-GOP, freezing
+# the client decode on one frame. punktfunk requests 8 MB SO_SNDBUF/SO_RCVBUF, but the kernel
+# clamps to these caps; raise them on the HOST for send-side headroom (the host logs a warning
+# when the grant is small). macOS clients need no tuning (their default cap is already multi-MB).
+#
+# Install:  sudo cp scripts/99-punktfunk-net.conf /etc/sysctl.d/ && sudo sysctl --system
+net.core.wmem_max = 8388608
+net.core.rmem_max = 8388608