feat(nav): show waypoint usage count in the list header

The Waypoints list header now reads "WAYPOINTS <n>/<cap>" (e.g. 3/16) so
it's clear at a glance how many waypoints are stored and how much room is
left before the table is full.

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

docs/solo_features/tools_screen/tools_screen.md

@@ -105,7 +105,7 @@ Cycle views with **LEFT / RIGHT**:
 
 ### Waypoints
 
-A waypoint is a saved spot — your car, camp, a water source — that you can navigate back to later. Waypoints are **independent of the trail**: they live in their own flash file (`/waypoints`), survive a reboot, and are **not** cleared by *Reset trail*. Up to 16 can be stored.
+A waypoint is a saved spot — your car, camp, a water source — that you can navigate back to later. Waypoints are **independent of the trail**: they live in their own flash file (`/waypoints`), survive a reboot, and are **not** cleared by *Reset trail*. Up to 16 can be stored — the Waypoints list header shows how many are in use (e.g. `WAYPOINTS 3/16`).
 
 **Dropping a waypoint** — **Hold Enter → Mark here**. This captures the current GPS fix and opens the on-screen keyboard for a short label (up to 11 characters — e.g. `CAR`, `CAMP`, `H2O`). Leaving it blank auto-names it `WP1`, `WP2`, … Marking works whether or not the trail is being recorded; it needs a GPS fix (otherwise it reports *No GPS fix*).
 

examples/companion_radio/ui-new/TrailScreen.h

@@ -508,7 +508,10 @@ private:
 
   void renderWpList(DisplayDriver& display) {
     display.setColor(DisplayDriver::LIGHT);
-    display.drawTextCentered(display.width() / 2, 0, "WAYPOINTS");
+    char title[24];
+    snprintf(title, sizeof(title), "WAYPOINTS %d/%d",
+             _task->waypoints().count(), WaypointStore::CAPACITY);
+    display.drawTextCentered(display.width() / 2, 0, title);
     display.fillRect(0, display.headerH() - 1, display.width(), display.sepH());
 
     int n     = wpListCount();