fix(grasp): sync visual-servo plane writes into perception singleton

Until Task 4 removes the duplicate WorkPlane code in grasp/visual_servo.py,
the visual-servo plane endpoints must also update perception.work_plane's
singleton so the below-plane filter (which reads from the perception side)
sees the newly-calibrated plane within the same process lifetime.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/presa_mano/api/grasp_routes.py

@@ -25,7 +25,12 @@ from ..grasp.visual_servo import (
 )
 from ..perception import ObjectDetector, filter_outliers, nuwa_to_cv_frame
 from ..perception.sam21_bridge import Sam21Fallback, points_via_sam21
-from ..perception.work_plane import apply_below_plane_filter, get_work_plane
+from ..perception.work_plane import (
+    WorkPlane as PerceptionWorkPlane,
+    apply_below_plane_filter,
+    get_work_plane,
+)
+from ..perception.work_plane import set_work_plane as _set_perception_work_plane
 from .perception_routes import _bbox_to_roi
 from ..timing import Stopwatch
 from . import _deps
@@ -341,6 +346,14 @@ def visual_servo_plane_fit(req: PlaneFitReq) -> dict[str, Any]:
         created_at=time.time(),
     )
     set_work_plane(wp)
+    # Keep perception.work_plane singleton in sync until Task 4 removes
+    # the visual-servo duplicate. Default offset_mm so the filter has a
+    # reasonable threshold without forcing the user through the new endpoint.
+    _set_perception_work_plane(PerceptionWorkPlane(
+        normal=wp.normal, offset=wp.offset, centroid=wp.centroid,
+        n_inliers=wp.n_inliers, fit_rms_mm=wp.fit_rms_mm,
+        roi=wp.roi, offset_mm=5.0, created_at=wp.created_at,
+    ))
     return {"ok": True, "plane": asdict(wp)}
 
 
@@ -353,4 +366,5 @@ def visual_servo_plane_get() -> dict[str, Any]:
 @router.delete("/visual_servo/plane")
 def visual_servo_plane_clear() -> dict[str, Any]:
     set_work_plane(None)
+    _set_perception_work_plane(None)
     return {"ok": True, "set": False}