refactor(unitree_g1): minimize diff w.r.t main

docs/SONIC_FIDELITY_TODO.md

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+# SONIC fidelity TODO — gaps vs gear_sonic / C++ deploy
+
+Remaining differences between this lerobot SONIC port and the original gear_sonic +
+`gear_sonic_deploy/g1_deploy_onnx_ref` reference. All three deployed encoder modes exist
+(0 locomotion, 1 three-point, 2 full-body SMPL); these are faithfulness gaps in *how*
+some pieces behave.
+
+## 1. 3-point calibration & source (mode 1)
+The original derives the 3 points from **full-body joints** and calibrates with
+`ThreePointPose` against **live measured robot joints** (`reset_with_measured_q`), plus
+neck→waist coupling. Our device path (head + controllers, fixed zero-q neutral) is an
+approximation.
+- Missing: measured-q recalibration + waist coupling.
+- Note: the body-source `compute_3point` path (needs PICO Motion Trackers) is already faithful.
+
+## 2. Locomotion stick/speed mapping (#6)
+gear_sonic's `PlannerLoop` uses a yaw-accumulator + **mode-dependent speed curves**
+(slow `0.1 + 0.5·mag`, run `1.5 + 3·mag`) with a facing-rotated movement vector. We reuse
+the keyboard-parity `apply_joystick_axes` (no speed-by-mode curve).
+- Also: PICO stick sign conventions untested (may need axis flips in `pico_publisher`).
+- Self-contained and sim-testable.
+
+## 3. Mode-2 root motion
+`enable_smpl_root=False` by default; the original feeds the SMPL root orientation into the
+anchor. Faithful only when enabled **and** the 30→50 Hz root trajectory is smoothed/
+rate-matched (currently causes base-acceleration spikes → NaN QACC).
+
+## 4. Start/stop handshake
+C++ has `WAIT_FOR_CONTROL` (operator "start" gate) and a "stop" halt. We start policy
+immediately after the startup ramp — no explicit arm/e-stop state machine.
+
+## 5. Startup ramp target
+C++ `InitControl` ramps to `default_angles`; we ramp to the policy's live commanded pose.
+Deliberate (per request) — only a gap if exact C++ parity is wanted.
+
+## 6. Hands / grippers
+Original maps trigger/grip → Dex3 hand joints in modes 1 & 2 (simple gripping: thumb open,
+trigger>0.5 closes middle finger, run through a gripper IK solver). Our 29-DOF path has no
+hand control.
+- Hardware here: **OpenArm grippers** (not Dex3) — could be routed through the same
+  trigger→open/close path, but needs the robot interface to expose/command the gripper
+  actuators (they're separate from the 29-DOF body).
+
+## Not gaps (settled)
+- `vr_5point_index` — vestigial constant in `policy_parameters.hpp`, not a deployed encoder
+  mode. Nothing to implement.
+- Action scaling, kp/kd, IsaacLab↔MuJoCo remaps, encoder cadence (encode ⅕ / decode 1×),
+  per-mode replan intervals (0.1/0.2/1.0), 8-frame cross-fade blend — all faithful.
+- Graceful damped shutdown — intentional safety addition, keep.
+
+## Suggested priority
+- High (change how the robot moves under teleop): #1, #2.
+- Medium: #3, #4, #6 (grippers).
+- Low / intentional: #5.