feat(l2,core): battery curve editor and an L2 feedback round

- Battery curve: NodePrefs batt_curve_mv[11] (voltage at 0..100 %, all
  zeros = built-in LiPo curve, sentinel 0xC0DE0032). ui-core/Battery.h
  uses it for every percentage. L1: Settings > System > Batt curve list
  (Left/Right 10 mV, Reset); L2: Settings > Power > Battery curve chart
  with draggable points and a line at the cell's voltage.
- L2: the Nodes map is the full navigation map plus the nodes, Back
  returns to Nodes; the favourite button is lit while it is one; pinning
  to the Home dial uses a thumbtack (fonts regenerated); minimap dots
  follow the accent; arranging tiles shows where they land while dragging;
  emoji row in Diagnostics > Font.
- Sim hooks: sim_open nodesmap / accent@N / homeedit / battcurve.

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

examples/companion_radio/ui-new/UITask.h

@@ -112,6 +112,7 @@ class UITask : public UITaskBase, public UiCoreHost {
   UIScreen* nearby_screen = nullptr;
   UIScreen* dashboard_config = nullptr;
   UIScreen* auto_advert_screen = nullptr;
+  UIScreen* batt_curve_screen = nullptr;
   UIScreen* live_share_screen = nullptr;
   UIScreen* locator_screen = nullptr;
   UIScreen* trail_screen = nullptr;
@@ -287,6 +288,7 @@ public:
   void gotoNearbyScreen();
   void gotoDashboardConfig();
   void gotoAutoAdvertScreen();
+  void gotoBatteryCurve();   // Settings > System > Battery curve
   void gotoLiveShareScreen();
   // Live share session control (ui-core/LiveShareEngine.h): restart = new
   // session (re-announce + fresh clock); clock-only = changed "Stop after".