feat(engine): Tiled P1 — rt_tmap model + GID resolver + render + projection (#69)

The heart of Tiled support: load a map and draw it.

- rt_tmap model (Tmap/TmLayer/TmTileset in tiled.ludic): map header + ordered
  layers (dense int32 GID arrays, heap-allocated to w*h, lifting the 96x64 cap)
  + tilesets. Built from the intermediate Value tree, so the TMX and TMJ paths
  both feed it.
- GID resolver (Tiled.resolve): gid -> (tileset, localId, flipH/V/D); the three
  flip flags masked off before the local-id lookup, returned alongside. gid==0
  is empty.
- Image-backed render (Tiled.draw): every visible tile layer in file order,
  blitting each tile from its tileset image with flips applied at draw.
- Compatibility projection (Tiled.project / auto on load): a designated
  collision layer projects to the legacy byte tilemap ('#' solid, '=' one-way
  via the oneway property, ' ' empty) so Grid.*/Path.*/esys_move are unchanged.
- Tiled.load resolves external tilesets + images relative to the map file and
  auto-projects a collision/solids/walls layer.
- The grid and physics_tiles demos now run off a loaded map (grid_maze.tmx /
  physics_map.tmx) instead of hand-authored Map.row strings, byte-identically.

Two compiler fixes fell out of this (see the changeset):
- emit_index_addr set g_addr_ty before evaluating the index, so slice[obj.field]
  came back mis-typed; set it last, like the raw-pointer branches.
- @strcmp was declared by both the world table and the fs prelude; centralise
  it in the head prelude so a game that uses Fs/Path links.

Proven by library/tiled_p1.ludic (14 assertions: loads+renders Kenney map
identically from .tmx and .tmj, flip mirroring) + the converted grid/
physics_tiles demos. x test: 92 passed; self-host bootstrap fixpoint intact.

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

examples/library/grid.ludic

@@ -7,13 +7,16 @@ program Grid {
   model Marker { Tag }
 
   handler Boot phase Start {
+    # The maze is now a loaded Tiled map (issue #69): its `collision` layer —
+    # 1 = wall, 0 = open — projects to the same byte tilemap Map.row used to fill,
+    # so every Grid.* / Path.* query below is byte-identical.
     #             01234567
-    Map.size(8, 5)
-    Map.row(0, "########")
-    Map.row(1, "#......#")
-    Map.row(2, "#.####.#")
-    Map.row(3, "#....#.#")
-    Map.row(4, "########")
+    #   row 0     ########
+    #   row 1     #......#
+    #   row 2     #.####.#
+    #   row 3     #....#.#
+    #   row 4     ########
+    Tiled.load("assets/tiled-fixtures/grid_maze.tmx")
 
     # --- Bresenham line ---
     let hl = Grid.line(1, 1, 6, 1)