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/editor/inspector/fieldFactory.ts

@@ -15,6 +15,7 @@ import {
   assetRefLabel,
   NO_ASSET_LABEL,
 } from '../../core/properties/assetRef';
+import { keyName } from '../../core/keys';
 import { FIRST_TILE_LAYER } from '../../core/model/liveTilemap';
 import { tilemapLayerNames } from '../../core/model/tilemap';
 import { isKindWith, type ReferenceKind } from '../../core/properties/kinds';
@@ -569,7 +570,7 @@ class KeyCaptureButton extends Button {
       this.capturing = true;
       return true;
     }
-    this.key = event.key;
+    this.key = keyName(event.key); // Shift + A is "a", the name the game hears it by
     this.setText(keyLabel(this.key));
     this.onCapture(this.key);
     return true;