describe_garden: list each plop's position, so a move can keep the layout

Asked to move four tomatoes planted in a column "keeping the same spacing",
the live assistant re-laid them as two pairs: the per-plop listing said
"north" and "south" and nothing else. Each listed plop (and list_plantings)
now carries xCm/yCm in the object's local frame.

Co-Authored-By: Claude Fable 5 <[email protected]>

internal/service/ops.go

@@ -610,15 +610,20 @@ type DescribeGroup struct {
 	Each []DescribePlanting `json:"each,omitempty"`
 }
 
-// DescribePlanting is one plop with a rough compass location. ID + Version let
-// an agent address a single plop — remove it or move it — the same way
-// DescribeObject.Version lets it edit an object.
+// DescribePlanting is one plop with its position and a rough compass location.
+// ID + Version let an agent address a single plop — remove it or move it — the
+// same way DescribeObject.Version lets it edit an object; XCM/YCM (the object's
+// local frame) let a move keep the layout the plops had, which "north, south"
+// alone cannot: asked to move four tomatoes in a column "keeping the same
+// spacing", the live assistant re-laid them as two pairs for want of these.
 type DescribePlanting struct {
 	ID        int64   `json:"id"`
 	Version   int64   `json:"version"`
 	PlantID   int64   `json:"plantId"`
 	Plant     string  `json:"plant"`
 	Count     int     `json:"count"`
+	XCM       float64 `json:"xCm"`
+	YCM       float64 `json:"yCm"`
 	Location  string  `json:"location"`
 	RadiusCM  float64 `json:"radiusCm"`
 	PlantedAt string  `json:"plantedAt,omitempty"`
@@ -736,7 +741,8 @@ func describeGroups(o *domain.GardenObject, plops []domain.Planting, plantByID m
 func describePlanting(pl domain.Planting, plantName string) DescribePlanting {
 	d := DescribePlanting{
 		ID: pl.ID, Version: pl.Version, PlantID: pl.PlantID, Plant: plantName,
-		Count: effectiveCount(pl), Location: describeLocation(pl.XCM, pl.YCM), RadiusCM: pl.RadiusCM,
+		Count: effectiveCount(pl), XCM: pl.XCM, YCM: pl.YCM,
+		Location: describeLocation(pl.XCM, pl.YCM), RadiusCM: pl.RadiusCM,
 	}
 	if pl.PlantedAt != nil {
 		d.PlantedAt = *pl.PlantedAt