Remote: match the old remote's hardware; old remote code in LEGACY

- LEGACY/remote/teensy/: old remote sketch from
  https://mangavalk.com/Hexapod/remote.git @ 492dece (reference only).
- remote/Config.h: sticks on A0-A5, Nextion on Serial1 (0/1), as in the
  old sketch; MPU6050 moved to Wire2 (25/24) since A4/A5 are Wire's pins.
- NextionUI: controls on a vscope-global "control" page added to the
  old HMI; keeps the old t1 status texts; the old page-1 b2 button (and
  serial 'U') enter Nextion upload passthrough, following the PC's baud.
- Docs: NEXTION.md, remote README wiring, CLAUDE.md.

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

2026-current/remote/SerialConsole.cpp

@@ -22,6 +22,7 @@ bool SerialConsole::poll(UiEvent& ui, Local& local) {
       case 'z': ui.cmd = UiCmd::ZeroGyro;          return true;
       case 'c': ui.cmd = UiCmd::CalStartSave;      return true;
       case 'x': ui.cmd = UiCmd::CalCancel;         return true;
+      case 'U': ui.cmd = UiCmd::NextionUpload;     return true;
       case 'p': local = Local::PrintStatus;        return true;
       case 'd': local = Local::ToggleDump;         return true;
       case 'R': local = Local::ResetCal;           return true;