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/ToolsScreen.h

@@ -21,7 +21,6 @@ public:
 
     int item_h  = display.lineStep();
     int start_y = display.listStart();
-    int cw      = display.getCharWidth();
     int vis     = display.listVisible(item_h);
     if (vis < 1) vis = 1;
 
@@ -29,18 +28,16 @@ public:
     if (_sel < _scroll)            _scroll = _sel;
     if (_sel >= _scroll + vis)     _scroll = _sel - vis + 1;
 
+    int reserve = scrollIndicatorReserve(display, ITEM_COUNT, vis);
     for (int i = 0; i < vis && (_scroll + i) < ITEM_COUNT; i++) {
       int idx = _scroll + i;
       int y   = start_y + i * item_h;
       bool sel = (idx == _sel);
-      display.drawSelectionRow(0, y - 1, display.width(), item_h, sel);
-      display.setCursor(0, y);
-      display.print(sel ? ">" : " ");
-      display.setCursor(cw + 2, y);
+      display.drawSelectionRow(0, y - 1, display.width() - reserve, item_h, sel);
+      display.setCursor(2, y);
       display.print(ITEMS[idx]);
     }
-    display.drawScrollArrows(start_y, start_y + (vis - 1) * item_h,
-                             _scroll > 0, _scroll + vis < ITEM_COUNT);
+    drawScrollIndicator(display, start_y, vis * item_h, ITEM_COUNT, vis, _scroll);
     return 500;
   }