fix(ui): gap below header separator, one method everywhere

Content drawn under the title separator touched the line on every standard
screen, because listStart() == headerH() (the row right after the separator).
Graphical screens worked around it with a hand-rolled hdr+2.

Bake a 2px breathing gap into listStart() so every list gains it at once, and
switch the screens that hand-rolled the offset (Compass, Nav, Nearby detail) to
listStart() so the content top is computed the same way everywhere.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/ui-new/CompassScreen.h

@@ -33,7 +33,6 @@ public:
     display.setColor(DisplayDriver::LIGHT);
     display.drawCenteredHeader("COMPASS");
 
-    const int hdr = display.headerH();
     const int cx  = display.width() / 2;
     const int ch  = display.getLineHeight();
     const int cw  = display.getCharWidth();
@@ -41,7 +40,7 @@ public:
     display.setTextSize(2);
     const int bigH = display.getLineHeight();
     display.setTextSize(1);
-    const int top      = hdr + 2;
+    const int top      = display.listStart();
     const int readout_y = display.height() - bigH - 1;   // size-2 readout baseline
     const int mid      = (top + readout_y) / 2;
 

examples/companion_radio/ui-new/NavView.h

@@ -37,7 +37,7 @@ inline void draw(DisplayDriver& d,
   geo::fmtDist(dist, sizeof(dist), dist_km, imperial);
 
   const int step = d.lineStep();
-  int y = hdr + 2;
+  int y = d.listStart();
 
   // Distance — emphasised at size 2.
   d.setTextSize(2);

examples/companion_radio/ui-new/NearbyScreen.h

@@ -404,7 +404,7 @@ class NearbyScreen : public UIScreen {
   // ── detail rendering ──────────────────────────────────────────────────────────
   void renderStoredDetail(DisplayDriver& display) {
     const Entry& e = _entries[_sel];
-    const int hdr  = display.headerH();
+    const int hdr  = display.listStart();   // content top (gap below the header separator)
     display.drawInvertedHeader(e.name);
 
     int step = display.lineStep();
@@ -434,7 +434,7 @@ class NearbyScreen : public UIScreen {
 
   void renderScanDetail(DisplayDriver& display) {
     const Entry& e = _entries[_sel];
-    const int hdr = display.headerH();
+    const int hdr = display.listStart();   // content top (gap below the header separator)
 
     char label[32];
     if (e.name[0]) { strncpy(label, e.name, 31); label[31] = '\0'; }

src/helpers/ui/DisplayDriver.h

@@ -39,7 +39,10 @@ public:
   // Use these instead of hardcoded pixel values so layouts adapt to any display.
   int lineStep()             const { return getLineHeight() + 2; }         // row pitch: text + gap
   int headerH()              const { return getLineHeight() + 3; }         // title bar height
-  int listStart()            const { return headerH(); }                   // y where list items begin
+  // y where list items begin: a 2px breathing gap below the header separator so
+  // the first row doesn't touch the line (matches the hand-rolled hdr+2 used by
+  // the graphical screens).
+  int listStart()            const { return headerH() + 2; }
   int listVisible(int itemH) const { return (height() - listStart()) / itemH; }
   int listVisible()          const { return listVisible(lineStep()); }
   // x where a right-side value column starts (leaves ~8 chars for the value)