Let a Sequence grow an output as you connect the last one

The Outputs setting is gone. A Sequence now keeps one free output below the
last connected one: nothing plugged in is one output, connecting the spare
grows a new one, unplugging the bottom edge shrinks it back.

It counts the last *connected* port rather than the number of edges, so
unplugging a middle one leaves a gap instead of silently dropping an edge.

Removing the setting also removes a bug it caused. Typing in the Outputs field
did nothing and the arrow keys did nothing, while dragging the value worked:
onInput fires per keystroke, the preview writes into node.params, that emits
'project', and Inspector.refreshValues() sees the node's signature change --
the port list is part of it -- so it rebuilds and destroys the row being typed
in. A drag survives because it keeps receiving globalpointermove on the old
widget. refreshValues() has no focus guard where refreshLive() does; the trap
is still there for the next typed field that changes a node's shape.

Ports that depend on the edges around a node mean derivePorts needs the graph,
not just the params, so resolveDef and portSignature take it too. And a node
whose ports are derived cannot know how many it has from its type, so run is
handed the definition resolved for it.

tests/helpers.ts

@@ -11,6 +11,7 @@ import {
   type PointerState,
   type Value,
   requireNodeDef,
+  type RunResult,
 } from '../src/core/graph';
 import type { BehaviorAsset, SceneAsset } from '../src/core/model/Asset';
 import { findObject, worldPosition } from '../src/core/model/hierarchy';
@@ -176,6 +177,17 @@ export function fakeContext(overrides: Partial<NodeContext> = {}): FakeContext {
   return ctx;
 }
 
+/** Runs a node on its registered definition: the shape it has while sitting in no graph. */
+export function runDef(
+  type: string,
+  ctx: NodeContext,
+  inputs: Record<string, Value>,
+  params: PropertyBag = {},
+): RunResult {
+  const def = requireNodeDef(type);
+  return def.run!(ctx, inputs, params, def);
+}
+
 /** Runs one node definition in isolation and returns its data outputs. */
 export function runNode(
   type: string,
@@ -183,7 +195,7 @@ export function runNode(
   params: PropertyBag = {},
   ctx: NodeContext = fakeContext(),
 ): Record<string, Value> {
-  return requireNodeDef(type).run!(ctx, inputs, params).outputs ?? {};
+  return runDef(type, ctx, inputs, params).outputs ?? {};
 }
 
 export interface WorldOptions {