Restoring gameplay scanline depth in the TD2 SDL port

Restoring gameplay scanline depth in the TD2 SDL port This checkpoint closed a very specific visual bug in the SDL reimplementation of The Duel: Test Drive II. The promoted gameplay rail gameplay_live_race_mid was still rendering from a flat end-of-frame ppu_state, which made the road swallow the shoulders and the horizon. That was good enough for early archaeology, but not for a faithful SNES-mimetic port. The fix was to stop treating that gameplay seed as one global presentation state. I attached the measured visible-scanline profile from tools/out/lane3_live_race_mid_scanline_full/td2_scanline_step_test.json directly to the promoted rail and fed these fields into the native SDL renderer: main_layers bg1_hscroll/bg1_vscroll bg2_hscroll/bg2_vscroll bg3_hscroll/bg3_vscroll That immediately restored the first-order depth cues on the live-race frame: the horizon comes back, BG3 only re-enters on the measured strip, and BG2 uses the real per-scanline staircase instead of one global VOFS.