fix: remove duplicate soften_forward definition (cherry-pick artifact)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/ai_mouse/_postprocess.py

@@ -92,42 +92,6 @@ def enforce_forward_monotonic(forward: np.ndarray) -> np.ndarray:
     return forward
 
 
-def soften_forward(
-    forward: np.ndarray,
-    backtrack_tol: float = 0.02,
-    overshoot_span: float = 0.08,
-) -> np.ndarray:
-    """Softly regularise the forward axis without destroying natural motion.
-
-    Real trajectories contain small backward corrections and overshoot
-    past the target; hard clipping turns both into visible artifacts
-    (stacked points, vertical walls). Instead:
-
-    - Backtracking is tolerated up to ``backtrack_tol``; larger dips are
-      raised to ``prev - backtrack_tol``.
-    - Values above 1.0 are compressed with tanh so they asymptote at
-      ``1 + overshoot_span`` (moderate overshoot survives, extremes
-      cannot fly far past the target).
-    - No lower clip: the endpoint warp pins the first point later.
-
-    Args:
-        forward: (T,) forward coordinates.
-        backtrack_tol: max allowed per-step regression.
-        overshoot_span: asymptotic max excess above 1.0.
-
-    Returns:
-        New (T,) array.
-    """
-    out = forward.copy()
-    for i in range(1, len(out)):
-        floor = out[i - 1] - backtrack_tol
-        if out[i] < floor:
-            out[i] = floor
-    over = out > 1.0
-    out[over] = 1.0 + overshoot_span * np.tanh((out[over] - 1.0) / overshoot_span)
-    return out
-
-
 def damp_start(lateral: np.ndarray, n: int = 4) -> np.ndarray:
     """Dampen lateral oscillation over the first ``n`` points, continuously.