Address Gadfly review on the garden copy

* api: detect an absent copy body by io.EOF from the decoder rather than
  Content-Length. A chunked request reports -1, not 0, so the length test
  read an empty chunked body as malformed and 400'd instead of taking the
  default-name path. Covered by a new unknown-length test.

* store: hoist the garden_objects/plantings INSERTs into shared
  objectInsert/plantingInsert statements with matching *InsertArgs
  helpers. CopyGarden had its own copies of both column lists, so a
  column added to the table could be wired into Create* and silently
  dropped from a copy.

* store: move the queryer interface to sqlite.go, next to the other
  shared query plumbing, instead of users.go.

* web: derive a copy's prefilled name via defaultCopyName, mirroring the
  server's copyName including its 200-BYTE cap. The inline
  `${name} (copy)` both duplicated the suffix and, for a garden whose
  name was already at the cap, prefilled an over-long name that the
  server rejected with a 400. Unit-tested, including multi-byte
  truncation on a code-point boundary.

* test: drop a throwaway `_ = kept`.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

internal/store/gardens.go

@@ -213,16 +213,7 @@ func (d *DB) CopyGarden(ctx context.Context, srcID, ownerID int64, name string)
 	// re-parented onto the right new object.
 	objectIDs := make(map[int64]int64, len(srcObjects))
 	for _, o := range srcObjects {
-		copied, err := scanObject(tx.QueryRowContext(ctx,
-			`INSERT INTO garden_objects
-			   (garden_id, kind, name, shape, points, x_cm, y_cm, width_cm, height_cm,
-			    rotation_deg, z_index, plantable, color, props, grid_size_cm, snap_to_grid, notes)
-			 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
-			 RETURNING `+objectColumns,
-			created.ID, o.Kind, o.Name, o.Shape, o.Points, o.XCM, o.YCM, o.WidthCM, o.HeightCM,
-			o.RotationDeg, o.ZIndex, boolToInt(o.Plantable), o.Color, o.Props,
-			o.GridSizeCM, boolToInt(o.SnapToGrid), o.Notes,
-		))
+		copied, err := scanObject(tx.QueryRowContext(ctx, objectInsert, objectInsertArgs(created.ID, &o)...))
 		if err != nil {
 			return nil, fmt.Errorf("store: copy object: %w", err)
 		}
@@ -243,11 +234,7 @@ func (d *DB) CopyGarden(ctx context.Context, srcID, ownerID int64, name string)
 			// Unreachable: every active planting joins an object we just copied.
 			return nil, fmt.Errorf("store: copy planting %d: source object %d not copied", p.ID, p.ObjectID)
 		}
-		if _, err := tx.ExecContext(ctx,
-			`INSERT INTO plantings (object_id, plant_id, x_cm, y_cm, radius_cm, count, label, planted_at)
-			 VALUES (?, ?, ?, ?, ?, ?, ?, ?)`,
-			objectID, p.PlantID, p.XCM, p.YCM, p.RadiusCM, p.Count, p.Label, p.PlantedAt,
-		); err != nil {
+		if _, err := scanPlanting(tx.QueryRowContext(ctx, plantingInsert, plantingInsertArgs(objectID, &p)...)); err != nil {
 			return nil, fmt.Errorf("store: copy planting: %w", err)
 		}
 	}