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/editor/graph/GraphCanvas.ts

@@ -235,7 +235,7 @@ export class GraphCanvas extends Widget {
     const seen = new Set<string>();
     const lookup = behaviorLookup(this.state.project);
     for (const node of asset.graph.nodes) {
-      const def = resolveDef(node, lookup);
+      const def = resolveDef(node, asset.graph, lookup);
       if (!def) continue;
       seen.add(node.id);
       let view = this.views.get(node.id);

src/editor/graph/paletteEntries.ts

@@ -1,6 +1,7 @@
 import {
   allNodeDefs,
   BEHAVIOR_PARAM,
+  createEmptyGraph,
   isTerminalType,
   type NodeDef,
   resolveDef,
@@ -39,7 +40,8 @@ export function paletteEntries(project: Project, asset: BehaviorAsset): PaletteE
     // A behavior running itself is an endless loop, so it is not on offer.
     if (other.type !== 'behavior' || other.id === asset.id) continue;
     const params = { [BEHAVIOR_PARAM]: other.id };
-    const def = resolveDef({ id: '', type: RUN_BEHAVIOR, x: 0, y: 0, params }, lookup);
+    // The entry is a preview of a node that sits in no graph yet, hence the empty one.
+    const def = resolveDef({ id: '', type: RUN_BEHAVIOR, x: 0, y: 0, params }, createEmptyGraph(), lookup);
     if (def) entries.push({ id: `${RUN_BEHAVIOR}:${other.id}`, hint: 'behavior', def, params });
   }
   return entries;