Let On key down repeat while the key stays held

A held key fired once and then nothing, so sliding a Tetris piece sideways or
walking a menu meant building a timer next to every key node. Two settings on
the node do it now: Repeat after and Repeat interval, both in milliseconds so
the usual values stay whole numbers (300, 50) instead of 0.3 and 0.05. A delay
of 0 keeps the node exactly as it was, an interval of 0 means every frame.

The browser's own auto-repeat is deliberately not used - Input.press has always
dropped it - because its delay and rate are an operating-system setting of the
player's, not a game's. The repeat is built from the measured hold time instead,
per node, so two nodes on one key keep their own clocks. The rule itself is a
pure function in keyRepeat.ts and is checked without a world.

Both rows stay off the node body while the delay is 0: two lines of "0" on every
key node in every graph would be noise, and the screenshot said so. NodeDef gains
hiddenParams for that; the inspector still shows them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tools/e2e/index.mjs

@@ -22,6 +22,7 @@ import { containerTab } from './16-container.mjs';
 import { editorRun } from './17-editor-run.mjs';
 import { pause } from './18-pause.mjs';
 import { nestedBehavior } from './19-nested-behavior.mjs';
+import { keyRepeat } from './20-key-repeat.mjs';
 
 export const STEPS = [
   hierarchy,
@@ -43,4 +44,5 @@ export const STEPS = [
   editorRun,
   pause,
   nestedBehavior,
+  keyRepeat,
 ];