Lift moves at the display's rate: render-time animation

Review (and the coordinator): Lift stepped with the core's 16 ms ticks, so
a 144 Hz display held each shadow for 2-3 refreshes. The lift springs are
now sampled at each frame's own time (p.now_ns), and Pardes.continuous()
reports a render-time animation in motion: while it is, the pump draws
every loop (a 1 ms wait takes only the input there is) and the present's
vsync paces it at the display's rate. They left nextWake; the stepped,
frame-indexed animations (transitions, message fades, the theme fade) and
every golden are unchanged. With PARDES_TEST_CLOCK, each loop of a moving
render-time animation moves the virtual clock by a display frame at
PARDES_TEST_HZ (default 60), so a 144 Hz series is deterministic: a focus
switch is 51 distinct frames at 144 Hz. Test: renders 6.9 ms apart give
rising lifts; settled, no frames. The tty never lifts (GUI capability).

Shared files touched: pardes.zig (continuous, pump), gui.zig.

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