docs: scaffold polisher-control foundation

docs/05-telemetry-channel-spec-v1.md

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+# Telemetry Channel Spec v1
+
+## Core channels — required at >=100 Hz
+
+```text
+timestamp_us
+table_angle_deg
+arm_angle_deg
+fz_n
+mx
+my
+mz
+spindle_rpm_actual
+table_rpm_actual
+arm_amplitude_deg_derived
+arm_center_deg_derived
+machine_state
+force_setpoint_n
+```
+
+## Strongly recommended channels
+
+```text
+fx_n
+fy_n
+ft_status
+z_servo_iq_v
+z_brake_engaged
+spindle_drive_state
+spindle_drive_error
+spindle_bus_voltage_v
+spindle_iq_a
+spindle_motor_temp_c
+arm_angle_linearized_deg
+table_rpm_setpoint
+spindle_rpm_setpoint
+force_actuator_cmd
+estop_active
+interlock_state
+mode
+fz_raw_n
+fz_contact_n
+```
+
+## Principles
+
+- One monotonic Teensy timestamp source.
+- Raw values, not only filtered values.
+- Commanded and actual values are both present.
+- Sensor validity is explicit; never substitute fake good values.
+- Gaps are detectable from timestamps.
+- Header names are stable because downstream analysis will depend on them.
+
+## CSV baseline
+
+First-write compatibility format is CSV. Later processing may produce Parquet/downsampled traces, but raw CSV must be preserved during commissioning.