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.

src/core/graph/nested.ts

@@ -41,12 +41,12 @@ export function declaredPorts(graph: Graph | undefined, type: string): PortDef[]
  * The node definition as it applies to *this* node: identical to the registered one, unless the
  * type declares ports per node (`declaresPorts`) or computes them (`derivePorts`).
  */
-export function resolveDef(node: GraphNode, lookup: BehaviorLookup): NodeDef | undefined {
+export function resolveDef(node: GraphNode, graph: Graph, lookup: BehaviorLookup): NodeDef | undefined {
   const def = nodeDef(node.type);
   if (!def || (!def.declaresPorts && !def.derivePorts)) return def;
   const own = def.declaresPorts ? (node.ports ?? []).map(portDefOf) : [];
   const side = (which: 'inputs' | 'outputs') => (def.declaresPorts === which ? own : []);
-  const grown = def.derivePorts?.({ params: node.params, behaviors: lookup }) ?? {};
+  const grown = def.derivePorts?.({ node, graph, behaviors: lookup }) ?? {};
   return {
     ...def,
     label: grown.label ?? def.label,
@@ -74,8 +74,8 @@ export function callProblem(node: GraphNode, lookup: BehaviorLookup, ownerId = '
  * Everything that changes how a node looks, as one string. Views and the inspector rebuild when it
  * changes – a port list that is derived rather than fixed has no other way of being noticed.
  */
-export function portSignature(node: GraphNode, lookup: BehaviorLookup, ownerId = ''): string {
-  const def = resolveDef(node, lookup);
+export function portSignature(node: GraphNode, graph: Graph, lookup: BehaviorLookup, ownerId = ''): string {
+  const def = resolveDef(node, graph, lookup);
   if (!def) return 'missing';
   const list = (ports: PortDef[]) => ports.map((p) => `${p.key}:${p.type}`).join(',');
   return `${node.type}|${def.label}|${list(def.inputs)}|${list(def.outputs)}|${