Gate controller pairing behind BOOTSEL

bootsel_pairing_button.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <cstdint>
+
+enum class BootselPairingButtonSample : uint8_t {
+    kUnread,
+    kReleased,
+    kPressed,
+};
+
+class BootselPairingButtonHoldFsm {
+public:
+    static constexpr uint8_t kHoldSamples = 20;
+
+    bool update(BootselPairingButtonSample sample);
+
+private:
+    uint8_t pressed_samples_ = 0;
+    bool hold_reported_ = false;
+};
+
+// Polls BOOTSEL at 10 Hz. Returns true once when a 20-sample hold completes.
+bool bootsel_pairing_button_task();