A transition carries a name, so a state needs no visible port (#52)

A state keeps its `in`/`out` exec pins in the model and the editor never draws
them. That is the whole trick: connecting, undo, deleting a state and saving all
keep working untouched, because `normalizeGraph` filters nodes and never edges,
and no edge ever checks its port key against a NodeDef. Only two places change --
`NodeView.redraw` stops drawing the row, and `portAt` refuses to hand one out, so
an invisible pin cannot be grabbed either.

Transitions are drawn by right-clicking a state, `Make transition`, then clicking
the target. The armed mode takes the same shape as a live drag, so the existing
preview draws it with no second code path, and it dies with Escape, a click on
empty canvas or a switch to another asset.

Removing the pins removed the only handle a transition had: edges have no
hit-test anywhere, and the pin right-click was the sole route to Disconnect.
The inspector's TRANSITIONS OUT / TRANSITIONS IN lists are therefore not a
convenience, they are the delete path.

`GraphEdge` gained an optional `label`, which `normalizeGraph` has to pass
through explicitly or a saved name is dropped on load. `State transition`
replaces `Next state`: it takes the machine on an input port and the name from a
picker, and resolves against the *current* state. Names are deliberately not
unique across a machine -- two states may both have an `alarm` -- so a node named
`alarm` moves whichever state has one, and an empty name follows the single
unnamed edge.

The geometry moved to a Pixi-free `transitions.ts`: a gap to the box border, and
a fan that puts a pair of opposite edges beside each other instead of on top of
each other. Keeping it as plain maths is what let a screenshot bug become a unit
test -- an earlier pin-to-pin line ran under the target node and took its
arrowhead with it, because `nodeLayer` sits above `edgeLayer`.

One limit stands and is not fixed here: `ConnectCommand` rejects a second edge
between the same two states ("Already connected"), because every transition
hangs off the same two ports. With names, `A --alarm--> B` beside
`A --seen--> B` is a sensible pair, so this is worth its own issue.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/commands/graphCommands.ts

@@ -242,6 +242,39 @@ export class FoldEdgeCommand implements Command {
   }
 }
 
+/** The name a transition answers to. Blank clears it, since an unnamed transition is the normal one. */
+export class NameTransitionCommand implements Command {
+  readonly label = 'Name transition';
+  private previous = '';
+
+  constructor(
+    private readonly assetId: string,
+    private readonly edgeId: string,
+    private readonly name: string,
+  ) {}
+
+  execute(project: Project): void {
+    const edge = this.edge(project);
+    this.previous = edge.label ?? '';
+    this.apply(edge, this.name.trim());
+  }
+
+  undo(project: Project): void {
+    this.apply(this.edge(project), this.previous);
+  }
+
+  private edge(project: Project): GraphEdge {
+    const edge = requireGraph(project, this.assetId).edges.find((e) => e.id === this.edgeId);
+    if (!edge) throw new CommandError(`Edge ${this.edgeId} not found`);
+    return edge;
+  }
+
+  private apply(edge: GraphEdge, name: string): void {
+    if (name) edge.label = name;
+    else delete edge.label;
+  }
+}
+
 /** One undo step for the whole selection; every node is found before any of them changes. */
 export class CollapseNodesCommand implements Command {
   readonly label: string;