feat(joint-router-avoid): worker.createWorker option and /worker subpath export

[kumilingus]

Description

WorkerProvider spawns its Web Worker with a hardcoded new Worker(new URL('./Worker.mjs', import.meta.url), { type: 'module' }). That only works when the consumer's bundler transforms this pattern inside node_modules (Vite, webpack 5). The Angular CLI esbuild builder transforms it only in application TS sources — at runtime the URL resolves against the main bundle (/Worker.mjs → 404), and hand-copying the file cannot work either, since it contains bare @joint/core / libavoid-js specifiers. The worker script URL was not configurable at all.

Changes

1. worker.createWorker option

initAvoidRouter(graph, {
    worker: {
        createWorker: () => new Worker(new URL('./my-avoid.worker', import.meta.url), { type: 'module' })
    }
});

The factory is stripped from the options posted to the Worker (a function cannot be structured-cloned). Default path unchanged — Vite/webpack consumers are unaffected.

2. @joint/router-avoid/worker subpath export

Public worker entry so the application-side worker file is one line — import '@joint/router-avoid/worker'; — and never references the private dist/ layout. Same pattern as pdfjs-dist and the Monaco editor workers.

Tests

TDD — written first and watched fail on dev: worker.createWorker overrides how the routing Worker is spawned (factory called once, provider talks to the factory-created Worker through the init/ready handshake, worker options forwarded). 29/29 passing; lint clean. Changeset: @joint/router-avoid minor.

The MainThreadProvider idle fix that briefly lived on this branch was split out to #3489 (patch, against master).

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