feat: Integrate bpmnlint

[jdehaan]

Fixes #83

Surface model validation issues directly in rendered diagrams and in the editor via bpmn-js-bpmnlint. A toggle button on the canvas shows clickable error/warning overlays on the offending elements.

• New lint attribute on : on | off | inactive.
• Plugin setting (defaults to off) to configure the default for the feature
• Linter enabled automatically on edits
• Rules live in .bpmnlintrc (extends bpmnlint:recommended) and are packed into the committed bundles at build time via bpmnlint-pack-config, since bpmnlint cannot resolve rules in the browser. build:vendor handles this automatically.
• The lint module runs in a plain Viewer (every injected service is present; editorActions resolves optionally), so no viewer upgrade was needed.
• Tests
• Translations

[alibama]

seems reasonable - my code review isn't worth the keystrokes here, but i'll acknowledge reading it and 👍 fwiw?

looks like internationalizing this for new languages won't be much work?

[jdehaan]

Yes indeed translation is a perfect job for LLMs
I focused on the feature and overlooked that. But adding the strings for the already provided languages is a good hint. I will do

[jdehaan]

Thanks for your contribution! I shipped the slightly reworked state. I hope others will enjoy. Likely there will be follow ups but I prefer always not going ahead of what people need, often the risk is to miss the point. Here the changes where mostly to keep the previous behavior by default to not upset people when they update the plugin. This is also a principle I try to follow when possible.