feat(nav/map): show two label characters beside a waypoint marker

One character was too ambiguous to tell adjacent waypoints apart on the
map. Draw the first two characters of the label (falling back to one when
the label is a single char) in both the normal and degenerate map paths,
and widen the right-edge fit guard to the rendered text width.

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

docs/solo_features/tools_screen/tools_screen.md

@@ -109,7 +109,7 @@ A waypoint is a saved spot — your car, camp, a water source — that you can n
 
 **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*).
 
-**On the map** — saved waypoints show on the Trail Map view as a hollow diamond with the label's first character beside it. The map's bounding box always includes them, so off-track waypoints stay in frame; the map even renders waypoints when no trail is recorded.
+**On the map** — saved waypoints show on the Trail Map view as a hollow diamond with the label's first two characters beside it (enough to tell nearby waypoints apart). The map's bounding box always includes them, so off-track waypoints stay in frame; the map even renders waypoints when no trail is recorded.
 
 **Navigating** — **Hold Enter → Waypoints** opens the list (each row shows the label and live distance). The list always begins with a synthetic **Trail start** row whenever a trail exists, so you can backtrack to where you began without having marked it. Select a row and press **Enter** to open the navigation view: