Give the graph a loop, and build Tetris with it

A Tetris example project needs to draw 200 board cells and scan rows
for a full line. Neither is expressible without iteration, so the node
system gets a Repeat node plus the missing text side: Substring, Find
text and To number. The interpreter drops its data cache once per
round -- otherwise every round would recompute with the first round's
values.

Object by name takes its name as an input now, not just as a setting;
addressing "c" + index is impossible otherwise. An unconnected input
reads the stored setting, so saved projects are untouched.

The board itself is a 200-character text, "." for empty. That makes
both operations of Tetris a single expression instead of a loop, and
each frame attempts exactly one move -- rotate beats sideways beats
fall -- so the fit check exists once in the whole graph.

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

src/core/graph/nodes/data/ToNumber.ts

@@ -0,0 +1,14 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { asNumber } from '../../values';
+import { any, num } from '../shared';
+
+export const ToNumber: NodeDef = {
+  type: 'ToNumber',
+  label: 'To number',
+  category: 'data',
+  description: 'Reads a text as a number. Anything that is not one – an empty text, a word – reads as 0.',
+  inputs: [any('value')],
+  outputs: [num('result')],
+  params: [],
+  run: (_ctx, inputs) => ({ outputs: { result: asNumber(inputs.value) } }),
+};