Add stall-based pingpong return mode and calibration improvements

- Add MIN_PWM_PERCENT (20%) to ensure motor starts reliably
- Add CURRENT_CALIBRATION factor (0.33) for accurate current readings
- Add stall-based return option for pingpong mode (returns on stall instead of time)
- Update stall detection: 7A threshold, 1000ms confirm time
- Add DISABLE_STALL_DETECT config option
- Keep last speed setting when motor stops (UI improvement)
- Update webserver UI with 'Return on stall only' checkbox

include/config.h

@@ -24,6 +24,7 @@
 #define PWM_RESOLUTION 8    // 8-bit resolution (0-255)
 #define PWM_CHANNEL_R 0     // LEDC channel for RPWM
 #define PWM_CHANNEL_L 1     // LEDC channel for LPWM
+#define MIN_PWM_PERCENT 20  // Minimum PWM when motor is running (%)
 
 // Current Sense Configuration
 // BTS7960 current sense ratio: 8500:1 (kilo-amps)
@@ -33,8 +34,10 @@
 #define SENSE_RESISTOR 1000.0f        // 1kΩ sense resistor (ohms)
 #define ADC_MAX 4095.0f               // 12-bit ADC max value
 #define ADC_VREF 3.3f                 // ADC reference voltage
-#define STALL_CURRENT_THRESHOLD 4.0f  // Current (amps) that indicates stall
-#define STALL_DETECT_TIME_MS 2500     // Time to confirm stall (ms) - accounts for startup inrush
+#define CURRENT_CALIBRATION 0.33f    // Calibration factor (measured current / reported current)
+#define STALL_CURRENT_THRESHOLD 7.0f  // Current (amps) that indicates stall
+#define STALL_DETECT_TIME_MS 1000     // Time to confirm stall (ms) - accounts for startup inrush
+#define DISABLE_STALL_DETECT false    // Set to true to disable stall detection
 
 // Web Server
 #define HTTP_PORT 80

include/motor.h

@@ -23,13 +23,14 @@ public:
     void setStallCallback(void (*callback)(float current));
     
     // Pingpong mode
-    void startPingpong(int speed, int timeMs, int speedRandomPercent, int timeRandomPercent);
+    void startPingpong(int speed, int timeMs, int speedRandomPercent, int timeRandomPercent, bool useStallReturn);
     void stopPingpong();
     bool isPingpongActive();
     int getPingpongSpeed();
     int getPingpongTime();
     int getPingpongSpeedRandom();
     int getPingpongTimeRandom();
+    bool getPingpongStallReturn();
 
 private:
     int _speed = 0;
@@ -50,6 +51,7 @@ private:
     int _pingpongCurrentTime = 2000;
     unsigned long _pingpongLastSwitch = 0;
     int _pingpongDirection = 1;
+    bool _pingpongUseStallReturn = false;  // Return only after stall detection
     
     void applyMotorState();
     float readCurrentSense(int pin);