udpscope: an oscilloscope view for a UDPStreamer source

GTK4 and libadwaita. It receives one UDP stream through the vendored
udpsclient, buffers it in a large ring, and draws it with the vendored
plotter: a trigger with a pre/post event window, a pause that freezes the
window, cursors, measurements, math channels in a node editor, an event cache,
named configurations, preferences, and an export of the visible window to
.npy/.csv. Waveform files can be opened and analysed in place.

The interface is two threads -- a producer that owns the socket and the GTK
main thread that owns every widget and the GL context -- sharing one model
under one mutex, with samples crossing through lock-free rings.

deps/plotter is a submodule pinned to the commit this tree builds against;
deps/udpsclient is vendored in place. docs/claude/ documents the rules that
cost a defect to learn, and SPECS.md is the requirement document.

src/ui/udpscope-ui.gresource.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- SPDX-License-Identifier: MIT -->
+<!-- SPDX-FileCopyrightText: 2026 Martino Ferrari -->
+<!--
+  The application's UI files, compiled into the binary beside the icons and the help pages, so there
+  is still exactly one file to run. `preprocess="xml-stripblanks"` is what catches a malformed file:
+  gtk_builder_new_from_resource() on a broken .ui returns nothing usable and the window simply does
+  not open, which is a silent failure at runtime and a loud one here.
+-->
+<gresources>
+  <gresource prefix="/org/udpscope/ui">
+    <file preprocess="xml-stripblanks">shortcuts.ui</file>
+  </gresource>
+</gresources>