perf(l2): long lists fill in over several loop passes

A widget costs ~1 ms on the L2, so Nodes with 48 rows held the screen for
~600 ms and a full contact list for over a second. fillStart() builds the
first screenful at once and fillTick() adds the rest ~25 ms a pass.

- Nodes: 6 rows first; the 2 s refresh rewrites built rows in place
- New message: contacts filled the same way
- Settings: a group at a time (all at once when coming back scrolled)
- Nodes 671 -> ~200 ms, Settings 376 -> ~190 ms longest UI stall

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

examples/companion_radio/ui-lvgl/UITask.h

@@ -322,7 +322,12 @@ private:
   void homeSwipePoll();
   void buildChats();
   void buildContacts();
+  void contactRow(int i);
+  void fillStart(lv_obj_t* list, int n, int first, void (UITask::*row)(int));
+  void fillTick();
   void buildSettings();
+  static const int SETTINGS_GROUPS = 5;
+  void settingsGroup(int i);
   void buildSchemaSettings();
   void schemaRows(lv_obj_t* body, uint8_t page);
   void showMapOptions(uint8_t section);
@@ -338,6 +343,8 @@ private:
   bool wifiInUse() const;   // a map download or an update holds the WiFi
   void buildNearby();
   void refreshNearbyList();
+  void nearbyRow(int i);
+  void nearbyRowSet(lv_obj_t* row, int i);
   uint32_t nearbySignature() const;
   void showScanPopup();
   void refreshScanPopup();