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/NodeRegistry.ts

@@ -1,6 +1,6 @@
 import type { PropertyBag, PropertyValue } from '../model/Properties';
 import type { PropertyDef } from '../properties/PropertySchema';
-import type { PortType } from './Graph';
+import type { Graph, GraphNode, PortType } from './Graph';
 import type { BehaviorLookup } from './lookup';
 import type { NodeContext } from './NodeContext';
 import { asBoolean, asNumber, asString, type Value } from './values';
@@ -42,9 +42,10 @@ export interface RunResult {
   call?: CallResult;
 }
 
-/** What a node may compute its ports from: its own settings, and the behaviors around it. */
+/** What a node may compute its ports from: itself, the graph it sits in, and the behaviors around it. */
 export interface PortSource {
-  params: PropertyBag;
+  node: GraphNode;
+  graph: Graph;
   behaviors: BehaviorLookup;
 }
 
@@ -83,8 +84,10 @@ export interface NodeDef {
   /**
    * Pure data nodes are evaluated on demand when a downstream input needs their value; exec nodes
    * run when the flow reaches them. Event nodes have no `run` – the interpreter seeds their outputs.
+   * `def` is this definition as resolved for the node at hand, which is the only way a node with
+   * derived ports can know how many it has.
    */
-  run?(ctx: NodeContext, inputs: Record<string, Value>, params: PropertyBag): RunResult;
+  run?(ctx: NodeContext, inputs: Record<string, Value>, params: PropertyBag, def: NodeDef): RunResult;
 }
 
 const defs = new Map<string, NodeDef>();