BDSP sim: tap replay, faked view changes, scene length #203

Part of #139.

#167's GridSim/StorySim can't catch three kinds of BDSP console failures yet (from the 2026-11-02 lessons). The whole-table run with end-tile checks (r75 Gate overshoot, r81 cave exit to the cliff) is being done separately; these are the rest.

• r80 tap test. GridSim already moves a tile on a 160 ms tap, but no test replays r80, where dpad_tiles walked one tile too far because the "turn" tap was a step. Add it, red with the old turn tap.
• A view-change signal the sim can fake. The walker counts taps by the screen changing, and the sim has no screen. Conveyors, TVs and cloud shadows (r84) were read as our movement 3+ times, and r67's quiet-then-moving tap was miscounted. Give the sim a "view moved" output with injectable scenery motion (moving while we stand, still while we move), so the walker's counting and any new movement signal can be tested offline.
• Scene length. r80's save "missed the menu" because Bebe's lines were still up when 01.07 ended. Model a scene as lasting N lines/seconds, so a step that ends before its scene does fails in the sim.

Done when each has a sim test shown red against the old behaviour, then green.