feat(engine): Tiled P5 — image/group layers, iso/hex/staggered coords, Wang (#73)

- Image layers: <imagelayer> renders with parallax + optional repeatx/repeaty
  tiling across the view; the image loads relative to the map file. Group layers
  flatten at build (children render in file order); layer offset/opacity/tint are
  queryable (Tiled.layer_kind / layer_offsetx / layer_offsety / layer_opacity /
  layer_tint), a group's tint applying recursively.
- Orientation transforms: Tiled.cell_x / Tiled.cell_y compute a tile cell's
  screen position for orthogonal, isometric ((x-y)*tw/2, (x+y)*th/2), staggered,
  and hexagonal (rows step by (tileh+hexsidelength)/2, alternate rows shoved per
  staggerindex) — the tile draw now places cells through them.
- Wang: exported Wang-set GIDs are ordinary GIDs and resolve through the standard
  GID resolver; the terrain-corner authoring concept is editor-side (design cut).

Proven by library/tiled_p5.ludic (14 assertions) over the real
isometric_grass_and_water.tmx (iso + Wang) and hexagonal-mini.tmx, plus a
hand-authored image+group fixture. x test: 96 passed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

selfhost/backend/emit_call.ludic

@@ -641,6 +641,14 @@ function emit_ns_call(ns: pointer, meth: pointer, e: Node) -> Val {
     if (meth == "template")     { bare = "tiled_read_template"; push(labels, "path") }
     if (meth == "spawn")        { bare = "tiled_spawn_object"; push(labels, "map"); push(labels, "object"); push(labels, "model") }
     if (meth == "spawn_layer")  { bare = "tiled_spawn_layer"; push(labels, "map"); push(labels, "layer"); push(labels, "model") }
+    # P5 (#73): orientation coords + image/group-layer accessors
+    if (meth == "cell_x")       { bare = "tmap_cell_sx";      push(labels, "map"); push(labels, "x"); push(labels, "y") }
+    if (meth == "cell_y")       { bare = "tmap_cell_sy";      push(labels, "map"); push(labels, "x"); push(labels, "y") }
+    if (meth == "layer_kind")   { bare = "tmap_layer_kind";   push(labels, "map"); push(labels, "layer") }
+    if (meth == "layer_opacity"){ bare = "tmap_layer_opacity"; push(labels, "map"); push(labels, "layer") }
+    if (meth == "layer_tint")   { bare = "tmap_layer_tint";   push(labels, "map"); push(labels, "layer") }
+    if (meth == "layer_offsetx"){ bare = "tmap_layer_offsetx"; push(labels, "map"); push(labels, "layer") }
+    if (meth == "layer_offsety"){ bare = "tmap_layer_offsety"; push(labels, "map"); push(labels, "layer") }
   }
   # #62: a package-provided namespace (declared with @Namespace(Foo)) that none
   # of the hardcoded core blocks matched — alias Foo.method to the bare function