ui: a signal's details sit directly under its name; its unit is user-changeable and saved with the session

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/layout_store.cpp

@@ -439,6 +439,7 @@ bool load_layout(const std::string& path, LayoutState& out) {
   st.window_s = 0.0;
   st.rows.clear();
   st.calibration.clear();
+  st.units.clear();
   st.colors.clear();
   st.enabled.clear();
   st.math.clear();
@@ -446,7 +447,7 @@ bool load_layout(const std::string& path, LayoutState& out) {
 
   std::string line;
   // What the last `[[...]]` header opened, so keys land in the right record.
-  enum class Section { Top, Plot, Calibration, Color, Math, Measure } section = Section::Top;
+  enum class Section { Top, Plot, Calibration, Unit, Color, Math, Measure } section = Section::Top;
   int plot_count = 0;
   bool plot_section_seen = false;
   while (std::getline(in, line)) {
@@ -460,6 +461,9 @@ bool load_layout(const std::string& path, LayoutState& out) {
       } else if (t == "[[calibration]]") {
         section = Section::Calibration;
         st.calibration.emplace_back();
+      } else if (t == "[[unit]]") {
+        section = Section::Unit;
+        st.units.emplace_back();
       } else if (t == "[[color]]") {
         section = Section::Color;
         st.colors.emplace_back();
@@ -686,6 +690,12 @@ bool load_layout(const std::string& path, LayoutState& out) {
         } catch (...) {
         }
       }
+    } else if (section == Section::Unit && !st.units.empty()) {
+      if (key == "name") {
+        st.units.back().name = strip_quote(value);
+      } else if (key == "unit") {
+        st.units.back().unit = strip_quote(value);
+      }
     } else if (section == Section::Color && !st.colors.empty()) {
       if (key == "name") {
         st.colors.back().name = strip_quote(value);
@@ -785,6 +795,9 @@ bool save_layout(const std::string& path, const LayoutState& state) {
     o << "\n[[calibration]]\nname = " << toml_escape(cal.name) << "\ngain = " << cal.gain
       << "\noffset = " << cal.offset << "\n";
   }
+  for (const auto& u : state.units) {
+    o << "\n[[unit]]\nname = " << toml_escape(u.name) << "\nunit = " << toml_escape(u.unit) << "\n";
+  }
   for (const auto& color : state.colors) {
     char rgb[16];
     std::snprintf(rgb, sizeof(rgb), "\"#%06X\"", color.rgb & 0x00FFFFFFu);