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>

src/core/graph/nodes/events/OnKeyDown.ts

@@ -1,12 +1,19 @@
 import type { NodeDef } from '../../NodeRegistry';
+import { asNumber } from '../../values';
 import { exec, keyParam } from '../shared';
 
 export const OnKeyDown: NodeDef = {
   type: 'OnKeyDown',
   label: 'On key down',
   category: 'event',
-  description: 'Runs once when the key is pressed.',
+  description: 'Runs when the key is pressed, and again while it stays held if a repeat is set.',
   inputs: [],
   outputs: [exec()],
-  params: [keyParam],
+  params: [
+    keyParam,
+    { key: 'repeatAfter', label: 'Repeat after (ms)', kind: 'number', default: 0, min: 0, step: 50 },
+    { key: 'repeatInterval', label: 'Repeat interval (ms)', kind: 'number', default: 0, min: 0, step: 10 },
+  ],
+  // Both rows go together: with no delay there is no repeat, so the interval is not in play either.
+  hiddenParams: (params) => (asNumber(params.repeatAfter ?? 0) > 0 ? [] : ['repeatAfter', 'repeatInterval']),
 };