feat(stdlib): Tiled P2 — collision normalisation into the Solids feed (#70)

Normalise three collision sources into the byte tilemap esys_move / Grid.* /
Path.* read, in the design's priority order (§3.5):

- per-tile <objectgroup> hitboxes (Tiled.tile_shapes) — the precise source;
- the solid/oneway/trigger bool property convention (Tiled.collision_kind);
- the designated collision layer — any non-zero GID solid (Tiled.project),
  the fallback source, applied automatically on load.

Tiled.collide drives collision from a visual layer's per-tile metadata alone
(a tile with no collision metadata stays passable). tmap_collision_kind
classifies a GID (0 none / 1 solid / 2 one-way / 3 trigger) from its metadata;
the projection adds the collision-layer fallback.

Proven by library/tiled_p2.ludic (14 assertions): kind classification for each
source, the property convention and collision-layer fallback producing an
identical Solids feed, a per-tile-<objectgroup> floor blocking an esys_move
mover, and A* over a loaded map matching the hand-authored baseline. x test:
93 passed.

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

assets/tiled-fixtures/p2_tiles.tsx

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Hand-authored collision-metadata tileset (issue #70). CC0. -->
+<tileset version="1.10" tiledversion="1.10.2" name="p2tiles" tilewidth="16" tileheight="16" tilecount="5" columns="5">
+ <tile id="1">
+  <objectgroup draworder="index">
+   <object id="1" x="0" y="0" width="16" height="16"/>
+  </objectgroup>
+ </tile>
+ <tile id="2"><properties><property name="oneway" type="bool" value="true"/></properties></tile>
+ <tile id="3"><properties><property name="solid" type="bool" value="true"/></properties></tile>
+ <tile id="4"><properties><property name="trigger" type="bool" value="true"/></properties></tile>
+</tileset>