feat(joint-router-avoid): new avoid router package

[kumilingus]

Supersedes #3443.

Summary

• Adds @joint/router-avoid, a new package that routes JointJS links via libavoid (WASM, through libavoid-js), keeping a graph's links obstacle-avoiding and orthogonally routed - no router: attribute needed once a link connects two elements. Ships both a main-thread provider and a Web-Worker-backed provider (worker: true) for larger graphs.
• Extracts the rightAngle router's path-finding into a new public @joint/core alg.rightAnglePath function, shared between the built-in rightAngle router and @joint/router-avoid's fallback route (used while avoid computes a link's real route, or when a link can't be routed by avoid at all). Fixes stale flat-property references left over from the bbox-based refactor that were breaking most of the rightAngle router's own test suite.
• Adds useModelGeometry to the rightAngle router's options.
• Adds examples/avoid-router-ts, a TypeScript demo app (simple graph, two independent RouterService instances on one dia.Graph, large graph routed via a Web Worker).
• Full TSDoc across the public and internal API.

API surface

• initAvoidRouter(graph, options) / loadAvoidRouter(filePath?) - entry points (also on the UMD global as joint.routers.avoid.*). The returned RouterService is not started: start()/stop() for continuous routing, routeAll()/routeSubgraph(cells) for one-shot passes (e.g. routing each container's content independently), isStarted, destroy().
• Positive filter callbacks trackLink/trackElement select what is routed/tracked as an obstacle.
• interceptUnroutableLink gives the consumer first refusal on a link avoid can't route, with a reason: 'unconnected' (loose end), 'untracked' (end element excluded via trackElement), or 'unsupported' (link-to-link connection).
• setRouteAttributes overrides how computed routes are applied (e.g. through a command manager), receiving origin: 'avoid' | 'fallback' and the provisional/final state; changeFlag names the opt flag marking the router's own writes.
• worker: boolean | { debounceTime?: number } runs libavoid inside a Web Worker; debounceTime controls how long the Worker batches incoming updates before processing them in one transaction.
• Events: link:routing, link:routed ({ origin, reason }), link:routing:cancelled, idle.

Test plan

• yarn test for @joint/router-avoid passes (28/28)
• @joint/core's test suite passes, including the previously-broken rightAngle router suite
• examples/avoid-router-ts type-checks (tsc --noEmit)
• Manual review of the libavoid integration (main-thread and Worker providers) against a real app

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