Painters put down white lines on the three new tennis courts at Spring St. in the Hudson River Park last Friday. “They want this done by hand, no over-spray, perfect corners — very expensive job,” noted one of the painters. The hard-surface courts will open by the middle of October, with a press conference marking the event. Chris Martin, spokesperson for the Hudson River Park Trust, the agency building the 5-mile-long waterfront park, said ground rules for use of the courts are still being worked out.