feat(stdlib): Tiled P4 — objects, custom props/types, templates, opt-in spawn (#72)

- Object layers: all shapes (rectangle/ellipse/point/polygon/polyline/text) and
  custom properties parse and are queryable — Tiled.object_count / Tiled.object /
  Tiled.object_shape, and Tiled.prop / prop_int / prop_type over any object /
  tile / layer / map.
- Custom types: Tiled.load_types reads an objecttypes.xml project custom-type
  table so a class property resolves its default; enum values resolve as strings.
- Templates: Tiled.template reads a .tx/.tj, and Tiled.load merges each object's
  `template` reference under the instance's overrides (field inheritance).
- Opt-in spawning: Tiled.spawn / Tiled.spawn_layer map an object's class +
  properties onto Ludic components through the reflection ABI (Position from x/y,
  each property to a like-named field). Off by default — no gameplay coupling in
  the core load. Split into tiled_spawn.ludic, spliced only for a Tiled *game*
  (the world table exists only under has_ecs), so a plain map-reading tool never
  links against the reflection ABI.

Proven by library/tiled_p4.ludic (18 assertions) incl. the design's named
orthogonal-outside.tmx object shapes. x test: 95 passed.

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

tools/docgen/inventory.json

@@ -701,6 +701,16 @@
     "tiled-tile_shapes",
     "tiled-draw_anim",
     "tiled-frame_gid",
-    "tiled-animated"
+    "tiled-animated",
+    "tiled-object_count",
+    "tiled-object",
+    "tiled-object_shape",
+    "tiled-prop",
+    "tiled-prop_int",
+    "tiled-prop_type",
+    "tiled-load_types",
+    "tiled-template",
+    "tiled-spawn",
+    "tiled-spawn_layer"
   ]
 }