fix(trail): map grid no longer silently disappears on elongated trails

A very elongated trail (lat_span << lon_span or vice-versa) shares an
isotropic scale, so the visible window in the *short* direction can span
many grid_m. The previous code computed lat_n / lon_n once and bailed
with `return` if either exceeded 40 — leaving the user with no grid at
all on east-west or north-south runs.

Now: after picking the initial step via the MIN_GRID_PX and shorter/2
loops, also bump the step up further until both lat_n and lon_n fit
within MAX_GRID_LINES (40). Falls back to `return` only if even the
largest STEPS[] entry (100 km) can't produce a small-enough grid — which
shouldn't happen in practice on terrestrial trails.

Also fixed: comment claimed "~4 intervals across shorter dim" while the
code divides by 3.0f. Updated to "~3 intervals" to match.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

FEATURES.md

@@ -413,6 +413,7 @@ Fix status after this pass:
 - ✅ M4 — `renderDiscoverDetail` skips pub-key line on very narrow displays
 - ✅ L1 — SNR shown with 0.25 dB precision everywhere
 - ✅ L4 — fallback `"?"` sender no longer memsets through `strncpy`
+- ✅ Trail map grid silent loss — when a very elongated trail makes `lat_n` or `lon_n` exceed 40, the renderer now bumps the step up instead of dropping the grid entirely. Comment fixed to match the `/ 3.0f` divisor ("~3 intervals", not 4). [`TrailScreen.h:505-565`](examples/companion_radio/ui-new/TrailScreen.h#L505-L565)
 - ❌ M1 — re-checked, not a bug (`default_scope_name[31]`)
 - 📋 H1 + H2 — still open; need coordinated fix in upstream `BaseChatMesh` (`findChannelIdx` should iterate `num_channels`, not `MAX_GROUP_CHANNELS`; `saveChannels` should stop at the first uninitialised slot) or a local override
 - 📋 H3 — left as known limitation pending UX call