refactor(ui): align screens to the documented UI conventions

Audit pass against docs/design/solo_ui_framework.md, converging deviations:

- prev/next: replace hand-rolled (c == KEY_LEFT || c == KEY_PREV) with
  keyIsPrev()/keyIsNext() in QuickMsgScreen, RingtoneEditor, TrailScreen,
  FullscreenMsgView. Two were real rotary-encoder gaps, not just style:
  NearbyScreen's filter and WaypointsView's hemisphere toggle used raw
  KEY_LEFT/RIGHT with no encoder twin, so the encoder couldn't drive them.
- NearbyScreen's list right column used a manual setCursor(width -
  getTextWidth(...)) instead of the existing drawTextRightAlign() helper
  (which also UTF-8-translates) — now uses it, like Diagnostics/Repeater.
- RepeaterScreen hand-rolled the whole drawList skeleton (scroll clamp +
  reserve + row loop + indicator); collapsed onto drawList().

No D-pad behaviour change; more uniform encoder support. Net -19 lines.

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

examples/companion_radio/ui-new/NearbyScreen.h

@@ -715,8 +715,7 @@ public:
           if (e.dist_km >= 0.0f) geo::fmtDist(right, sizeof(right), e.dist_km, useImperial());
           else                   strncpy(right, "?GPS", sizeof(right));
         }
-        display.setCursor(display.width() - display.getTextWidth(right) - 2 - reserve, y);
-        display.print(right);
+        display.drawTextRightAlign(display.width() - reserve - 2, y, right);
       });
     }
 
@@ -779,8 +778,8 @@ public:
       _detail_refresh_ms = millis();
       return true;
     }
-    if (c == KEY_LEFT)  { _filter = (_filter + F_COUNT - 1) % F_COUNT; refresh(); return true; }
-    if (c == KEY_RIGHT) { _filter = (_filter + 1) % F_COUNT;          refresh(); return true; }
+    if (keyIsPrev(c)) { _filter = (_filter + F_COUNT - 1) % F_COUNT; refresh(); return true; }
+    if (keyIsNext(c)) { _filter = (_filter + 1) % F_COUNT;          refresh(); return true; }
     return false;
   }
 };