feat(admin): local-device mode + reuse Nodes screen for target picking

Tools > Admin now opens on a This-device / Remote-node chooser. "This
device" is a login-free 2-tab carousel (System: Name/Radio/TX power/
Lat/Lon, Actions: Send advert/Reboot) mapped onto NodePrefs/sensors and
reusing Settings' own apply chains -- no CommonCLI port. "Remote node..."
opens Tools > Nodes in a pick-mode (borrow-another-screen's-list idiom),
and Nodes gains an "Admin" Hold-Enter action; both converge on the single
canonical UITask::openAdminFor() -> AdminScreen::startFor().

Also:
- KeyboardWidget: opt-in PlaceholderRefreshFn hook for contextual {}-key
  CLI command-name completion (word-replacing); default behaviour and all
  other keyboard uses unchanged.
- TabBar: ellipsize() re-measures the real "text..." candidate per step
  (+ width clamp) so dots can't spill into a neighbour/reserved icon.
- ChannelsView: form rows truncate instead of wrapping.
- Reboot moved off the default-selected Actions row (fires with no confirm).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/ui-new/UITask.h

@@ -231,6 +231,8 @@ public:
   void gotoRingtoneEditor(int slot = 0);
   void gotoBotScreen();
   void gotoAdminScreen();
+  void pickAdminTarget();                  // open Nodes to choose a remote repeater/room for Admin
+  void openAdminFor(const ContactInfo& ci); // canonical Admin entry for a specific target (Nodes' Hold-Enter menu or the picker above)
   void gotoNearbyScreen();
   void gotoDashboardConfig();
   void gotoAutoAdvertScreen();