Remove all LED pulsing - returning to stable baseline

Pulsing code was causing crashes (FastLED.show() RMT conflict with USB).
Removed:
- update() is now empty no-op (was calling mux_ptr->show() every 33ms)
- Removed set_bpm(), beat_interval_ms, bpm serial command
Kept:
- Per-pad LED colors with dim off state (working fine)
- All button/MIDI/expression pedal functionality

src/main.cpp

@@ -89,13 +89,6 @@ void handle_serial_command(const String& cmd) {
     } else if (cmd == "exp") {
         Serial.printf("[CMD] EXP ADC=%d MIDI=%d\n",
                       exp_pedal.get_raw(), exp_pedal.get_value());
-    } else if (cmd.startsWith("bpm ")) {
-        uint16_t bpm = cmd.substring(4).toInt();
-        if (bpm >= 20 && bpm <= 300) {
-            led_driver.set_bpm(bpm);
-        } else {
-            Serial.println("[CMD] BPM must be 20-300");
-        }
     } else if (cmd == "usb") {
         Serial.printf("[CMD] USB mounted: %s\n", TinyUSBDevice.mounted() ? "YES" : "NO");
         Serial.printf("[CMD] USB ready: %s\n", TinyUSBDevice.ready() ? "YES" : "NO");
@@ -140,7 +133,6 @@ void handle_serial_command(const String& cmd) {
         Serial.println("  red/green/blue - solid colour");
         Serial.println("  pixel0/pixel1 - single pixel test");
         Serial.println("  exp        - expression pedal ADC/MIDI value");
-        Serial.println("  bpm <n>    - set LED pulse tempo (20-300, default 120)");
         Serial.println("  usb        - USB connection status and descriptor info");
         Serial.println("  gpiotest   - raw GPIO pin diagnostic");
         Serial.println("  rawled     - bit-bang WS2812 (no library)");
@@ -364,9 +356,6 @@ void setup() {
     Serial.println("[INIT] Initializing Expression Pedal...");
     exp_pedal.begin();
     
-    Serial.println("[INIT] Setting LED pulse tempo...");
-    led_driver.set_bpm(120);
-
     Serial.println("[INIT] Registering MIDI callbacks...");
     controller.begin();