Delete the JRPG's collision too, and wall the map with proxies

cell_solid and feet_blocked go, and so does the prediction in the player's
movementlogicfunc. That prediction was only ever exact because the town has zero
gravity and zero drag -- v is t, so `x + tx * dt` is where the step lands. A map
with gravity would have had to fold ey in as well, which is the game
re-implementing the integrator. Resolution runs after the move now, so there is
nothing to predict.

The map's decoration layer carries `collidable`, which retires JRPG_LAYER_SOLID:
akgl_TilemapLayer has no name member, so the game and the map had to agree on an
index out of band and inserting a layer in Tiled broke it.

The edge of the world is not on any layer, so it is four static proxies covering
the outer ring plus a tile of overhang -- one pool slot per side instead of a
hundred solid tiles, and the first use of the static-proxy path in either
example. They carry LAYER_STATIC explicitly: shape_box defaults a shape to
LAYER_ACTOR, and a wall left on that layer is a wall everything walks through.

Only the player gets a shape. NPCs stand still and are spoken to; the follower
is a child snapped to its parent every step.

Verified against the old implementation with the demo script rewritten to hold
one direction: holding left into a building stops the player at x=122 with both,
and holding up into the map's edge stops them at y=-4 with both.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KzBDV2fqgnUAcqCKqKvc71

docs/tutorials/assets/jrpg/town.tmj

@@ -1227,7 +1227,14 @@
    "visible": true,
    "width": 30,
    "x": 0,
-   "y": 0
+   "y": 0,
+   "properties": [
+    {
+     "name": "collidable",
+     "type": "bool",
+     "value": true
+    }
+   ]
   },
   {
    "draworder": "topdown",