ui: the trigger panel offers a noise band and an HF reject

Two label-only rows in trigger-panel.ui (band_row, hf_row, after holdoff_row and before
mode_row) and the two spins the code appends into them: the band on the level spins' scale
in signal units, the HF reject at 0-1e7 Hz with 0 off. Both are published with the other
fields -- read before the model lock is taken, assigned inside it -- and both join the
value-changed loop, so editing either republishes the condition.

The rows are shown per type: the band for every type but Dropout, which is an absence a
band cannot describe, and the HF reject for all of them, since it sits before every
comparison. `sync_trigger_rows()` resolves a row as its spin's parent rather than keeping a
second handle to it: the row comes from the file and holds one child.

The exit dump counts the panel's controls, so it reads controls_inside=15/15 now -- and the
probe confirms it, along with both search readings and no Gtk-CRITICAL:

    [udpscope] trigger panel: boxes=15 controls_inside=15/15 search_widgets=4/4 search_inside=4/4

src/ui/trigger-panel.ui

@@ -162,6 +162,30 @@
         </child>
       </object>
     </child>
+    <child>
+      <object class="GtkBox" id="band_row">
+        <property name="orientation">horizontal</property>
+        <property name="spacing">6</property>
+        <child>
+          <object class="GtkLabel">
+            <property name="label" translatable="yes">noise band</property>
+            <property name="halign">start</property>
+          </object>
+        </child>
+      </object>
+    </child>
+    <child>
+      <object class="GtkBox" id="hf_row">
+        <property name="orientation">horizontal</property>
+        <property name="spacing">6</property>
+        <child>
+          <object class="GtkLabel">
+            <property name="label" translatable="yes">HF reject Hz</property>
+            <property name="halign">start</property>
+          </object>
+        </child>
+      </object>
+    </child>
     <child>
       <object class="GtkBox" id="mode_row">
         <property name="orientation">horizontal</property>