Sloped walls with a flat 45° face, and diagonal wall lines (t36)

- New Sloped wall piece: a half-block triangle in any wall material, at half a wall's cost.
  Dragging walls or slopes at about 45° lays a diagonal line; the drag picks the slope's
  orientation and T flips or turns it.
- Each slope fills one cell past its corner, so a diagonal run is sealed against grains and water.
- New test/t_slopes.js: a slope funnel passes 400/400 sand (square steps 379/400).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/sim/blueprints.js

@@ -27,7 +27,7 @@ function flipBlueprint(bp) {
     : code === BP_PUMP || code === BP_OUTLET ? (((v & 3) === 1 ? 3 : (v & 3) === 3 ? 1 : v & 3) | (v & 4)) : v;
   return {
     v: 2, bw, bh: bp.bh, name: bp.name,
-    blocks: bp.blocks.map(([x, y, c, v, e]) => e ? [bw - 1 - x, y, c, flipV(c, v), e] : [bw - 1 - x, y, c, flipV(c, v)]),
+    blocks: bp.blocks.map(([x, y, c, v, e]) => e ? [bw - 1 - x, y, isSlope(c) ? BP_SLOPE_BL + ((c - BP_SLOPE_BL) ^ 1) : c, flipV(c, v), e] : [bw - 1 - x, y, isSlope(c) ? BP_SLOPE_BL + ((c - BP_SLOPE_BL) ^ 1) : c, flipV(c, v)]),
     machines: bp.machines.map(([t, x, y, d]) => {
       const P = PIECE_BY_ID[t];
       let nd = d;