Add SysEx handling for Launchpad X Programmer mode

- Parse all SysEx CIN types (start, continue, end)
- Reassemble multi-packet SysEx messages
- Handle layout select (Programmer mode = 0x7F)
- Handle Programmer/Live mode switch

src/app_task.cpp

@@ -50,6 +50,14 @@ void AppTask::process_midi_event(const MidiEvent& event) {
     // (visible without serial when connected to iPad)
     led_driver->flash_activity();
     
+    if (event.type == MidiEvent::SYSEX) {
+        // Cin is encoded in channel for SYSEX packets
+        uint8_t cin = event.channel;
+        uint8_t packet[3] = {event.data1, event.data2, 0};
+        process_sysex_packet(packet, cin);
+        return;
+    }
+
     uint8_t led_index = 0xFF;
     uint8_t midi_channel = event.channel;
     uint8_t midi_note = event.data1;
@@ -137,3 +145,54 @@ void AppTask::process_switch_event(uint8_t switch_id, bool pressed) {
         }
     }
 }
+
+void AppTask::process_sysex_packet(const uint8_t* packet, uint8_t cin) {
+    // Cin values: 0x4=start/short, 0x5=continue, 0x6=end (2 bytes), 0x7=end (1 byte/3 bytes)
+    
+    if (cin == 0x4) {  // SysEx start
+        sysex_active = true;
+        sysex_len = 0;
+    }
+    
+    if (!sysex_active || sysex_len >= SYSEX_MAX_LEN) return;
+    
+    // Add data bytes (skip F0/F7 which are handled by Cin)
+    sysex_buffer[sysex_len++] = packet[0];
+    if (cin == 0x4 || cin == 0x5 || cin == 0x6) {
+        sysex_buffer[sysex_len++] = packet[1];
+    }
+    
+    if (cin == 0x6 || cin == 0x7) {  // SysEx end
+        sysex_active = false;
+        handle_sysex(sysex_buffer, sysex_len);
+        sysex_len = 0;
+    }
+}
+
+void AppTask::handle_sysex(const uint8_t* data, uint8_t len) {
+    if (len < 7) return;
+    
+    // Check Novation SysEx header: F0 00 20 29 02 0C/0D ...
+    if (data[0] != 0x00 || data[1] != 0x20 || data[2] != 0x29 || data[3] != 0x02) {
+        return;
+    }
+    
+    uint8_t sub_id = data[4];
+    uint8_t command = data[5];
+    
+    Serial.printf("[APP] SysEx: sub=%02X cmd=%02X len=%d\n", sub_id, command, len);
+    
+    // Command 0x00 = Layout select, 0x0E = Programmer/Live mode
+    if (command == 0x00 && len >= 7) {  // Layout select
+        uint8_t layout = data[6];
+        Serial.printf("[APP] Layout select: %02X\n", layout);
+        
+        // 0x7F = Programmer mode
+        if (layout == 0x7F) {
+            Serial.println("[APP] Entered Programmer mode");
+        }
+    } else if (command == 0x0E && len >= 7) {  // Programmer/Live mode
+        uint8_t mode = data[6];
+        Serial.printf("[APP] Programmer mode: %02X\n", mode);
+    }
+}