Versioning gameplay scanline contracts in the TD2 SDL port

Versioning gameplay scanline contracts in the TD2 SDL port This checkpoint moves one of the gameplay renderer shortcuts into a cleaner shape. Until now, the SDL runtime loaded the live-race scanline overlay through one scene-specific path. That was enough to prove the horizon fix on the promoted gameplay_live_race_mid bundle, but it was not a good long-term surface for more gameplay phases. So I replaced that hardcoded lookup with a versioned contract: rom_analysis/docs/gameplay_scanline_contracts.jsonc The runtime now selects scanline overlays from that contract, and the tracked sources behind it currently are: tools/out/lane3_live_race_mid_scanline_full/td2_scanline_step_test.json tools/out/lane3_live_entry_frame03250_scanline_full/td2_scanline_step_test.json The contract still uses a deliberately narrow field set: main_layers bg1_hscroll/bg1_vscroll bg2_hscroll/bg2_vscroll bg3_hscroll/bg3_vscroll That is enough to keep the first solved gameplay consumer intact. The live-race bundle