Initial import: robot firmware + PlatformIO two-env scaffold

Robot-side firmware (Teensy 4.0) imported unchanged as extracted.
platformio.ini defines [env:robot] (teensy40) and [env:remote]
(teensy41); scripts/select_src_dir.py points each env at its own
sketch folder so robot/ and remote/ stay Arduino-style sketches.

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

2026-current/robot/StateMachine.h

@@ -0,0 +1,17 @@
+#pragma once
+
+enum class RobotState { DISARMED, SIT, STAND, WALKING };
+
+class StateMachine {
+public:
+  void begin() { state_ = RobotState::DISARMED; blend_ = 0; }
+  void update(bool armed_request, bool stand_request, bool walk_active_request, float dt);
+
+  RobotState state() const { return state_; }
+  float sitStandBlend() const { return blend_; }   // 0 = sit pose, 1 = stand pose
+
+private:
+  RobotState state_ = RobotState::DISARMED;
+  float blend_ = 0;
+  static constexpr float BLEND_RATE = 1.0f;   // per second - full sit->stand in ~1s
+};