fix(routers.rightAngle): allow zero-value margins and un-clamp minPathMargin

[Geliogabalus]

Summary

• rightAngle router used || for margin, sourceMargin, and targetMargin, so 0 was silently coerced back to the default (20/margin) instead of being honored.
• minPathMargin was clamped with Math.min(opt.minPathMargin, sourceMargin/targetMargin), so it could only ever narrow the overlap-detection zone, never widen it beyond margin.
• Both are now resolved with ??, so 0 is respected and minPathMargin can be set larger than margin to intentionally widen the detour-detection zone.
• Rewrote the right-angle-playground-js example into an interactive demo with live sliders for sourceMargin, targetMargin, and minPathMargin, visualizing each margin as a band around the elements/link.

Test plan

• Added tests covering margin: 0, sourceMargin: 0, and targetMargin: 0.
• Added a test demonstrating minPathMargin larger than margin actually changes the route.
• Renamed the pre-existing (mistyped) minMargin test option to minPathMargin and adjusted element positions so the "with"/"without" assertions in each of those tests actually diverge instead of asserting identical paths.
• grunt karma:joint passes for test/jointjs/routers.js (66/66); full joint suite shows only 2 pre-existing, unrelated failures (util.breakText ellipsis, port labels label attributes).
• eslint clean on the modified test file.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adjusts the rightAngle router option handling in @joint/core so zero-valued margins are honored and minPathMargin can widen (not just narrow) the overlap-detection zone. It also updates router tests accordingly and rewrites the right-angle-playground-js example into an interactive, visual demo for tuning these margins.

Changes:

• Use nullish coalescing (??) for margin, sourceMargin, and targetMargin, and stop clamping minPathMargin to per-side margins.
• Update/add QUnit coverage for margin: 0, sourceMargin: 0, targetMargin: 0, and minPathMargin > margin, plus rename prior minMargin test usage to minPathMargin.
• Rework the right-angle-playground-js example into a slider-driven demo that visualizes margin bands.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/joint-core/src/routers/rightAngle.mjs	Updates router option defaults so 0 is respected and minPathMargin is no longer clamped.
packages/joint-core/test/jointjs/routers.js	Adjusts/extends tests to cover zero-margins and widened minPathMargin, and aligns naming with the public option.
examples/right-angle-playground-js/index.html	Adds a toolbar UI for live-tuning margin-related router options.
examples/right-angle-playground-js/src/main.js	Implements interactive router option binding and margin visualization on elements/link.
examples/right-angle-playground-js/src/styles.css	Adds toolbar/control styling and updates the demo’s look/feel.

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