Stop a key getting stuck when Shift changes it while held (#227)

Input remembered keys under KeyboardEvent.key. Pressing a, adding
Shift and letting go sent "A" on release, which matched nothing, so
"a" stayed down until the next release without Shift.

- New rule keyName in src/core/keys.ts lowercases a single character.
  So a and A are the same key, also under Caps Lock.
- Input remembers per physical key (e.code) under which name it went
  down and releases exactly that name. So 1 released as ! is freed
  too, which lowercasing alone does not cover.
- On key down, up and held, Key is down and Axis input compare with
  the same rule. A node that already stores A reacts to a.
- Recording a key in the inspector stores Shift+A as a.
- Limit: holding Shift before pressing 1 still sends !, and a node on
  1 does not react. Nothing gets stuck by it.

Tests:
- 3 new unit tests in tests/core/behavior-events.test.ts: the flow
  from the issue, 1 released as !, and a node on A hearing a.
- Without lowercasing exactly the issue test and the A test fail.
- Without the code memory exactly the 1/! test fails.
- ./check.sh: 159 files, 2340 tests, CHECK EXIT 0 (before 2337).
- No e2e change, the check sum stays at 1377.

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

src/runtime/systems/BehaviorSystem.ts

@@ -22,6 +22,7 @@ import {
   type Value,
 } from '../../core/graph';
 import { stepKeyRepeat } from '../../core/graph/keyRepeat';
+import { keyName } from '../../core/keys';
 import { graphLookup } from '../../core/model/graphLookup';
 import { type PropertyBag, textOf, type Vec2 } from '../../core/model/Properties';
 import { findAssetOf, findScene, type Project } from '../../core/model/Project';
@@ -436,7 +437,7 @@ export class BehaviorSystem implements System {
 
   update(world: World, dt: number): void {
     this.syncInstances(world);
-    const keyOf = (node: { params: PropertyBag }) => textOf(node.params.key ?? '');
+    const keyOf = (node: { params: PropertyBag }) => keyName(textOf(node.params.key ?? ''));
     const frozen = world.frozen;
     for (const instance of this.instances) {
       if (!world.entities.includes(instance.entity)) continue; // destroyed this frame, reaped below
@@ -490,7 +491,7 @@ export class BehaviorSystem implements System {
    * in `nodeState`, so two nodes on the same key repeat on their own schedules.
    */
   private fireKeyDown(i: GraphInterpreter, ctx: NodeContext, node: GraphNode, dt: number): void {
-    const key = textOf(node.params.key ?? '');
+    const key = keyName(textOf(node.params.key ?? ''));
     const stored = i.nodeState.get(node.id);
     const { state, fires } = stepKeyRepeat(
       stored ? { held: stored.held ?? 0, repeats: stored.repeats ?? 0 } : null,