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/plot_host.cpp

@@ -252,9 +252,23 @@ void RowSet::install(Row& r, int /*row_index*/, plot::Plot& p) {
   // `Figure::link_x()` refuses a member whose x axis still follows on its own.
 }
 
+void RowSet::set_row_weights(std::vector<float> weights) {
+  // The count is not checked here: `apply_row_weights()` sizes it to the rows that exist, so a layout
+  // with rows added or removed keeps working instead of silently losing its sizing.
+  row_weights_ = std::move(weights);
+  if (figure_ != nullptr) apply_row_weights();
+}
+
+void RowSet::apply_row_weights() {
+  if (row_weights_.empty() || figure_ == nullptr) return;
+  row_weights_.resize(static_cast<std::size_t>(rows_), 1.0f);
+  (void)figure_->set_row_weights(row_weights_);
+}
+
 void RowSet::rebuild_all() {
   figure_ = std::make_unique<plot::Figure>(static_cast<plot::u32>(rows_));
   figure_->set_row_gap(kRowGap);
+  apply_row_weights();
   x_group_ = figure_->add_x_link();
   for (int i = 0; i < kMaxRows; ++i) {
     Row& r = row(i);