docs: scaffold polisher-control foundation

firmware/teensy/include/polisher_telemetry.h

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+#pragma once
+#include <stdint.h>
+
+struct FT_LoadSample {
+    float Fx;
+    float Fy;
+    float Fz;
+    float Mx;
+    float My;
+    float Mz;
+    uint32_t status;
+};
+
+struct TelemetrySample {
+    uint64_t timestamp_us;
+    float table_angle_deg;
+    float arm_angle_deg;
+    float fz_n;
+    float mx;
+    float my;
+    float mz;
+    float spindle_rpm_actual;
+    float table_rpm_actual;
+    float arm_amplitude_deg_derived;
+    float arm_center_deg_derived;
+    uint8_t machine_state;
+    float force_setpoint_n;
+};