feat(ui): GPS breadcrumb phase 1 — storage, sampling, Summary view

Adds Tools › Breadcrumb. Enter on the screen toggles tracking; while
active, UITask::loop samples GPS at the cadence chosen in settings
(default 1 min) and drops the point into a 256-entry RAM ring guarded
by a min-distance gate (default 25 m). A "G" indicator joins "A" in
the status bar with the same blink convention.

New storage:
- examples/companion_radio/Breadcrumb.h — BreadcrumbStore class
- 256 × 12 B = 3 KB RAM (survives auto-off, lost on reboot — explicit
  flash-slot save comes in phase 4)
- Haversine min-delta gate, total distance, elapsed seconds, current
  km/h, bounding-box helper

New screen:
- examples/companion_radio/ui-new/BreadcrumbScreen.h — Summary view
  with Status, Points, Dist (m or km), Time (h:mm), Speed; Enter
  toggles tracking, Esc returns to Tools

Schema bump 0xC0DE0002 → 0xC0DE0003 for two new NodePrefs bytes:
breadcrumb_interval_idx (1min default) and breadcrumb_min_delta_idx
(25m default). Older saves leave both at zero, which matches the new
defaults. DataStore::loadPrefsInt/savePrefs read/write the pair.

Logging on/off is a runtime flag inside BreadcrumbStore — not a
preference — so reboot returns to the off state cleanly; the user
will be able to persist a snapshot to a slot in phase 4.

Phase 2 (map view), 3 (point list), 4 (slot save/load, GPX export over
USB), and 5 (settings UI) follow incrementally.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/companion_radio/DataStore.cpp

@@ -305,6 +305,8 @@ void DataStore::loadPrefsInt(const char *filename, NodePrefs& _prefs, double& no
   }
 
   rd(_prefs.favourite_contacts, sizeof(_prefs.favourite_contacts));
+  rd(&_prefs.breadcrumb_interval_idx,  sizeof(_prefs.breadcrumb_interval_idx));
+  rd(&_prefs.breadcrumb_min_delta_idx, sizeof(_prefs.breadcrumb_min_delta_idx));
 
   // Schema sentinel: bumped on layout changes. Mismatch means an older file
   // (or a different schema); rd() already zero-inits any fields not present,
@@ -403,6 +405,8 @@ void DataStore::savePrefs(const NodePrefs& _prefs, double node_lat, double node_
     file.write((uint8_t *)&_prefs.eink_full_refresh_every, sizeof(_prefs.eink_full_refresh_every));
     file.write((uint8_t *)&_prefs.page_order_set, sizeof(_prefs.page_order_set));
     file.write((uint8_t *)_prefs.favourite_contacts, sizeof(_prefs.favourite_contacts));
+    file.write((uint8_t *)&_prefs.breadcrumb_interval_idx,  sizeof(_prefs.breadcrumb_interval_idx));
+    file.write((uint8_t *)&_prefs.breadcrumb_min_delta_idx, sizeof(_prefs.breadcrumb_min_delta_idx));
 
     // Tail sentinel — must be last. See NodePrefs::SCHEMA_SENTINEL.
     uint32_t sentinel = NodePrefs::SCHEMA_SENTINEL;