feat(map): packet flow - what the radio hears, as lines between nodes

Every packet heard runs from its origin through the repeaters with a
position to this device; a packet sent is a ring. ui-core/PacketFlow.h
resolves them (UiCore::flow, MyMesh logRx/logTx -> Listener). ui-lvgl
draws them on the map's marker layer and repaints only their area while
they move; ui-new draws the last minute on the Nodes map ("Flow" in its
options). Setting: Map options > On the map > Packet flow, CLI map.flow.
Off by default. Sim-checked only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/companion_radio/NodePrefs.h

@@ -540,6 +540,9 @@ struct NodePrefs {  // persisted to file
   // 1 = latest message first, 2 = by name. See chanctl::order().
   static const uint8_t CH_SORT_COUNT = 3;
   uint8_t  ch_sort;
+  // Map > options > "Packet flow": what the radio hears drawn on the map as
+  // lines between the nodes (ui-core/PacketFlow.h). 0 = off (default).
+  uint8_t  flow_show;
 
   // Single source of truth for the live-share option tables (shared by the Map
   // UI labels and the auto-send engine in UITask).