Let a tile report a touch instead of blocking it (#160)

A tile could be solid, one-way and scaled, but not report without
blocking. Water, lava, spikes or a goal zone needed a trigger object
of their own laid over the map. Now a tile has a switch Trigger, and
the collision events name the tile and the cell they met.

- A tile has the switch "Trigger (reports, never blocks)" under
  Solid. Its cells hold nothing up: no Move, no falling body, no
  ray. They raise On collision enter, stay and exit with the tilemap
  as other.
- The three events have the outputs tile, cell x and cell y. Without
  a tile, tile is empty and the cell is -1, -1.
- The three events have the input per cell. Off, the default, gives
  one event per area: cells of the same tile that touch side by
  side. On gives one event per cell.
- The scene view outlines trigger cells in yellow like a trigger
  collider, merged to rectangles but never with solid cells.
- Is touching with the map counts trigger tiles, and Set tile works
  while the game runs.
- Both systems find the touches with the same overlap check in
  runtime/systems/tileTriggers.ts, not through the physics engine.

Decided here:

- Trigger wins over Solid. A tile with both does not block, as with
  a collider.
- Water beside lava is two areas, and so are two ponds that touch
  only at a corner.
- An area names the cell nearest to the centre of the collider, and
  on exit the cell it named last.
- The solid cells of a map still do not name their tile.
- Normal, impulse and point are 0, as with a trigger collider.
- Collision scale and outlines shape a trigger cell like a solid
  one. One-way, friction and bounciness have no effect.

Tests:
- Gate on stein2: 205 files, 3104 tests (3067 + 37), exit 0
- e2e 39,40: 106 checks. e2e 1-8,39-43: 490 checks. Both on
  melektaus-atx. No full run, the sum of 1648 (1645 + 3) is
  reckoned and CI measures it.
- 37 unit tests in tests/core/tile-triggers.test.ts, nearly all
  against both systems
- Three e2e checks with a real mouse in block 40l-iv
- 24 unit counter-probes fail tests. Two did not at first, tests
  were added for them.
- Two browser counter-probes fail their checks
- Two screenshots looked at (yellow outline, the node with per cell)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/core/graph/GraphInterpreter.ts

@@ -120,6 +120,17 @@ export class GraphInterpreter {
     this.follow(node, port, ctx, 0);
   }
 
+  /**
+   * A data input of an event node, read ahead of its pulse: what decides whether the event concerns
+   * the node at all (#160). Null for an input the node does not have.
+   */
+  eventInput(node: GraphNode, key: string, ctx: NodeContext): Value {
+    this.frame = this.emptyFrame(this.graph);
+    this.steps = 0;
+    const port = this.def(node)?.inputs.find((p) => p.key === key);
+    return port ? this.inputValue(node, port, ctx) : null;
+  }
+
   /**
    * The `On state entered` / `On state exited` nodes watching one machine. A node whose machine
    * input carries a running value rather than a pick has no state outputs at all, so it is never