Split wiring, drags and the frame layer out of GraphCanvas (#215)

GraphCanvas had grown to 1406 lines. Wiring, dragging and the frame
views each carry their own state, so they now live in their own
classes behind a narrow host interface. Behaviour is unchanged.

- GraphCanvasHost is what the new classes see of the canvas.
- Wiring owns dragging a pin, the palette on a drop into empty space
  and "Make transition".
- GraphDrags owns moving nodes and frames, including snapping.
- AnnotationLayer holds the frame views. The test hooks stay on the
  canvas and read the views through the layer.
- BeadClock moves into beads.ts and can now be tested without a
  browser.
- The canvas builds host, wiring and drags in its constructor because
  state is a parameter property and not set during field init.
- GraphCanvas is down to 1019 lines.

Tests:
- ./check.sh: 145 files, 2192 tests, CHECK EXIT 0 (+2 for BeadClock)
- e2e 1-28,31,36: ALL PASSED, 932 checks
- New e2e check in 36k: a frame caught by the rubber band is also
  drawn as selected. No check covered that before. Against a bent
  build it fails with selected: false.
- Counter-checks for drop target, snapping and beads fail exactly
  the expected checks.
- Editor check sum is now 1314 (CI measured 1313 at 487b3aa).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/graph/graphHost.ts

@@ -0,0 +1,31 @@
+import type { AddNodeCommand } from '../../core/commands/graphCommands';
+import type { GraphAsset } from '../../core/model/Asset';
+import type { Box } from '../framing';
+import type { EditorState } from '../state';
+import type { NodeView } from './NodeView';
+import type { PaletteEntry } from './paletteEntries';
+import type { Point } from './transitions';
+
+/** What the graph canvas lends the gestures that work inside it. */
+export interface GraphCanvasHost {
+  readonly state: EditorState;
+  /** The asset on the canvas; empty when there is none. */
+  assetId(): string;
+  asset(): GraphAsset | null;
+  views(): ReadonlyMap<string, NodeView>;
+  /** Views in stacking order, topmost first – a node drawn over another one wins the pointer. */
+  topDownViews(): Iterable<NodeView>;
+  nodeUnder(global: Point): string | null;
+  /** Each node as the rectangle it is actually drawn as. */
+  nodeBoxes(): Box[];
+  /** The graph point under a global pointer position. */
+  toGraph(global: Point): Point;
+  /** Screen pixels per graph unit. */
+  zoom(): number;
+  snapping(): boolean;
+  /** What the palette offers for this graph. */
+  entries(): PaletteEntry[];
+  /** The command that adds a node from the palette at a graph point. */
+  newNode(entry: PaletteEntry, at: Point): AddNodeCommand;
+  redraw(): void;
+}