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/editor/graph/NodeView.ts

@@ -199,7 +199,9 @@ export class NodeView extends Widget {
     return this.toGlobal({ x: PAD + CHEVRON_SLOT / 2, y: TITLE_HEIGHT / 2 });
   }
 
+  /** Rows of ports, which set the node's height – none on a state, whose ports are never drawn. */
   private rowCount(): number {
+    if (this.def.transitionEdges === true) return 0;
     return Math.max(this.def.inputs.length, this.def.outputs.length);
   }
 
@@ -275,9 +277,12 @@ export class NodeView extends Widget {
     return this.headerHeight() + index * ROW_HEIGHT + ROW_HEIGHT / 2;
   }
 
-  /** Every port with its local centre – none while collapsed, so none can be grabbed. */
+  /**
+   * Every port with its local centre – none while collapsed, and none on a state, so neither can
+   * be drawn or grabbed. `portPosition` stays open either way: the edges still need their anchor.
+   */
   private *portCentres(): Iterable<{ port: PortDef; isOutput: boolean; x: number; y: number }> {
-    if (this.collapsed) return;
+    if (this.collapsed || this.def.transitionEdges === true) return;
     for (const [list, isOutput] of [
       [this.def.inputs, false],
       [this.def.outputs, true],