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/SmoothedValue.h

@@ -0,0 +1,25 @@
+#pragma once
+
+// Rate-limited setpoint smoother. Every place a discrete command can jump
+// (body pose axes, gait speed, the sit/stand blend) gets one of these instead
+// of using the raw commanded value directly.
+struct SmoothedValue {
+  float current = 0;
+  float target  = 0;
+  float max_rate;   // units per second
+
+  explicit SmoothedValue(float rate = 100.0f) : max_rate(rate) {}
+
+  void setTarget(float t) { target = t; }
+
+  float update(float dt) {
+    float delta = target - current;
+    float max_step = max_rate * dt;
+    if (delta > max_step) delta = max_step;
+    else if (delta < -max_step) delta = -max_step;
+    current += delta;
+    return current;
+  }
+
+  void reset(float v) { current = target = v; }
+};