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/NodeRegistry.ts

@@ -14,11 +14,23 @@ export interface PortDef {
 
 export type NodeCategory = 'event' | 'flow' | 'data' | 'variable' | 'action';
 
+/**
+ * How a loop node asks for one of its exec outputs to be run repeatedly: `port` carries the body,
+ * `index` is the number output seeded with the round number.
+ */
+export interface RepeatResult {
+  port: string;
+  index: string;
+  times: number;
+}
+
 export interface RunResult {
   /** Cached for the rest of the pulse. */
   outputs?: Record<string, Value>;
   /** Exec output(s) to continue along; omitted = the node ends the flow. */
   next?: string | string[];
+  /** Runs `port` that many times before continuing along `next`. */
+  repeat?: RepeatResult;
 }
 
 /** Palette, port rendering, connection validation and inspector fields are all derived from this. */