feat(ui): proportional scrollbar with mini-icon caps; reclaim row space

Replace the text ^/v scroll arrows with a font-scaling indicator drawn in
icons.h: a proportional thumb between fixed up/down triangle mini-icon caps.
drawScrollIndicator() lives in a ~5px right-edge column and scales via
miniIconScale (1x OLED, 2x landscape e-ink).

- Mini-icons: ICON_SCROLL_UP/DOWN; miniIconDrawTop (exact placement) and
  miniIconDrawHalo (shape-hugging 1px DARK halo, clip_top to spare the header
  separator) so caps stay visible on the LIGHT selection bar without a box.
- Thumb is 3*s wide so it centres on the triangle column; caps are static end
  markers (always drawn) so neither vanishes at the extremes.
- scrollIndicatorReserve(): right-edge gutter (0 when the list fits). Content,
  the selection bar and the message-history bubbles are all narrowed by it so
  nothing renders under the scrollbar. Portrait e-ink wrap width subtracts the
  reserve in both the box-height pass and render so wrapped text can't spill.
- Drop the redundant ">" selection marker (the highlight bar already shows
  selection) and shift rows to x=2, reclaiming left-edge space.
- Wire the indicator into every scrollable list (Bot, Settings, Nearby, Tools,
  Trail, QuickMsg lists + DM/channel history) and add one to WaypointsView,
  which scrolled with no indicator before.

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

examples/companion_radio/ui-new/TrailScreen.h

@@ -412,9 +412,7 @@ private:
       display.print(buf);
     }
 
-    display.drawScrollArrows(y0, y0 + (visible - 1) * step,
-                             _summary_scroll > 0,
-                             _summary_scroll + visible < SUMMARY_ITEM_COUNT);
+    drawScrollIndicator(display, y0, visible * step, SUMMARY_ITEM_COUNT, visible, _summary_scroll);
   }
 
   void renderList(DisplayDriver& display) {
@@ -466,8 +464,7 @@ private:
       display.print(row);
     }
 
-    display.drawScrollArrows(top, top + (visible - 1) * step,
-                             _list_scroll > 0, _list_scroll + visible < total);
+    drawScrollIndicator(display, top, visible * step, total, visible, _list_scroll);
   }
 
   // Shared map projection: geographic (1e-6 deg) → screen pixels. The scale is