Add stateful HD-rumble decoder with TinyUSB report normalization

Decode Nintendo HD-rumble words once in firmware into conventional low/high magnitudes and normalize stripped control SET_REPORT vs complete interrupt OUT reports through one path.

switch_haptics.h

@@ -0,0 +1,46 @@
+#ifndef SWITCH_HAPTICS_H
+#define SWITCH_HAPTICS_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+struct SwitchRumbleOutput {
+    uint8_t low_frequency_magnitude;
+    uint8_t high_frequency_magnitude;
+};
+
+size_t normalize_switch_output_report(uint8_t report_id,
+                                      const uint8_t* payload,
+                                      size_t payload_size,
+                                      uint8_t output[64]);
+
+class SwitchHapticsDecoder {
+public:
+    SwitchHapticsDecoder();
+
+    void reset();
+    SwitchRumbleOutput decode(const uint8_t payload[8]);
+
+private:
+    struct ActuatorState {
+        uint8_t high_amplitude;
+        uint8_t low_amplitude;
+        uint8_t high_frequency;
+        uint8_t low_frequency;
+        uint32_t last_word;
+        bool have_last_word;
+    };
+
+    struct AmplitudePeak {
+        uint8_t low;
+        uint8_t high;
+    };
+
+    static void reset_actuator(ActuatorState& state);
+    static AmplitudePeak decode_actuator(ActuatorState& state, uint32_t word);
+    static uint8_t amplitude_to_magnitude(uint8_t amplitude_index);
+
+    ActuatorState actuators_[2];
+};
+
+#endif