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.cpp

@@ -1471,6 +1471,16 @@ void UITask::gotoToolsScreen()     { setCurrScreen(tools_screen); }
 void UITask::gotoBotScreen()       { setCurrScreen(bot_screen); }
 void UITask::gotoAdminScreen()     { setCurrScreen(admin_screen); }  // AdminScreen::onShow() resets it
 void UITask::gotoNearbyScreen()    { setCurrScreen(nearby_screen); }
+
+void UITask::pickAdminTarget() {
+  setCurrScreen(nearby_screen);   // runs NearbyScreen::onShow()'s reset first
+  ((NearbyScreen*)nearby_screen)->startPickAdminTarget();
+}
+
+void UITask::openAdminFor(const ContactInfo& ci) {
+  setCurrScreen(admin_screen);   // runs AdminScreen::onShow()'s reset first
+  ((AdminScreen*)admin_screen)->startFor(ci);
+}
 void UITask::gotoDashboardConfig() { setCurrScreen(dashboard_config); }
 void UITask::gotoTrailScreen()     { setCurrScreen(trail_screen); }
 void UITask::gotoCompassScreen()   { setCurrScreen(compass_screen); }