feat(ui): v1.13 — collapsible Settings, Favourites Dial, GPX trail, schema fix

- SettingsScreen: collapsible sections (Enter toggles); all collapsed by default;
  vis[] filtered list drives render and UP/DOWN/Enter navigation
- NodePrefs: bump SCHEMA_SENTINEL 0xC0DE0003 → 0xC0DE0004; reset trail_units_idx
  in mismatch handler (was corrupted on upgrade from 0003 saves)
- UITask: shorten "No contacts available" → "No fav contacts" (OLED alert overflow)
- README: document Favourites Dial, GPS Trail + GPX download instructions,
  Mark-all-read, collapsible Settings; update USB/BLE export note

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

examples/companion_radio/DataStore.cpp

@@ -327,6 +327,10 @@ void DataStore::loadPrefsInt(const char *filename, NodePrefs& _prefs, double& no
     if (_prefs.home_pages_mask != 0) {
       _prefs.home_pages_mask |= NodePrefs::HP_FAVOURITES;
     }
+    // 0xC0DE0003 → 0xC0DE0004: trail_units_idx added after trail_min_delta_idx.
+    // Saves from 0xC0DE0003 have the sentinel bytes where trail_units_idx sits,
+    // so rd() picks up 0x03 (low byte of the old sentinel) — reset to default 0.
+    _prefs.trail_units_idx = 0;
   }
 
   file.close();