Add pingpong mode with speed, time, and randomness settings

- Add pingpong oscillation mode that alternates motor direction
- Settings: base speed (10-100%), time before return (0.5-10s)
- Randomness controls for both speed (0-50%) and time (0-50%)
- Web UI with sliders and start/stop buttons
- API endpoints: /pingpong/start and /pingpong/stop
- Real-time status polling shows pingpong active state

src/motor.cpp

@@ -78,6 +78,9 @@ void MotorController::update() {
     // Check for stall condition
     checkStall();
 #endif
+    
+    // Update pingpong mode
+    updatePingpong();
 }
 
 int MotorController::getSpeed() {
@@ -154,6 +157,89 @@ float MotorController::readCurrentSense(int pin) {
 #endif
 }
 
+// Pingpong mode implementation
+void MotorController::startPingpong(int speed, int timeMs, int speedRandomPercent, int timeRandomPercent) {
+    _pingpongBaseSpeed = constrain(speed, 0, 100);
+    _pingpongBaseTime = constrain(timeMs, 100, 30000);
+    _pingpongSpeedRandomPercent = constrain(speedRandomPercent, 0, 100);
+    _pingpongTimeRandomPercent = constrain(timeRandomPercent, 0, 100);
+    
+    _pingpongDirection = 1;
+    _pingpongCurrentSpeed = applyRandomness(_pingpongBaseSpeed, _pingpongSpeedRandomPercent);
+    _pingpongCurrentTime = applyRandomness(_pingpongBaseTime, _pingpongTimeRandomPercent);
+    _pingpongLastSwitch = millis();
+    _pingpongActive = true;
+    
+    // Apply initial state
+    _speed = _pingpongCurrentSpeed;
+    _direction = _pingpongDirection;
+    applyMotorState();
+    
+    Serial.printf("Pingpong started: speed=%d%% (base=%d, rand=%d%%), time=%dms (base=%d, rand=%d%%)\n",
+                  _pingpongCurrentSpeed, _pingpongBaseSpeed, _pingpongSpeedRandomPercent,
+                  _pingpongCurrentTime, _pingpongBaseTime, _pingpongTimeRandomPercent);
+}
+
+void MotorController::stopPingpong() {
+    _pingpongActive = false;
+    stop();
+    Serial.println("Pingpong stopped");
+}
+
+bool MotorController::isPingpongActive() {
+    return _pingpongActive;
+}
+
+int MotorController::getPingpongSpeed() {
+    return _pingpongBaseSpeed;
+}
+
+int MotorController::getPingpongTime() {
+    return _pingpongBaseTime;
+}
+
+int MotorController::getPingpongSpeedRandom() {
+    return _pingpongSpeedRandomPercent;
+}
+
+int MotorController::getPingpongTimeRandom() {
+    return _pingpongTimeRandomPercent;
+}
+
+void MotorController::updatePingpong() {
+    if (!_pingpongActive) return;
+    
+    unsigned long now = millis();
+    if ((now - _pingpongLastSwitch) >= (unsigned long)_pingpongCurrentTime) {
+        // Time to switch direction
+        _pingpongDirection = -_pingpongDirection;
+        
+        // Apply randomness for next cycle
+        _pingpongCurrentSpeed = applyRandomness(_pingpongBaseSpeed, _pingpongSpeedRandomPercent);
+        _pingpongCurrentTime = applyRandomness(_pingpongBaseTime, _pingpongTimeRandomPercent);
+        _pingpongLastSwitch = now;
+        
+        // Apply new state
+        _speed = _pingpongCurrentSpeed;
+        _direction = _pingpongDirection;
+        applyMotorState();
+        
+        Serial.printf("Pingpong switch: dir=%d, speed=%d%%, next_time=%dms\n",
+                      _pingpongDirection, _pingpongCurrentSpeed, _pingpongCurrentTime);
+    }
+}
+
+int MotorController::applyRandomness(int baseValue, int randomPercent) {
+    if (randomPercent == 0) return baseValue;
+    
+    int maxVariation = (baseValue * randomPercent) / 100;
+    int variation = random(-maxVariation, maxVariation + 1);
+    int result = baseValue + variation;
+    
+    // Ensure result stays positive and reasonable
+    return max(1, result);
+}
+
 void MotorController::checkStall() {
 #if CURRENT_SENSING_ENABLED
     // Only check stall when motor should be running