[mahach666]

What changes and why

IfcIO's job is reading and writing IFC. Several extras grew around it; this PR states which of them are frozen (bug fixes only, no new features or options) and what is planned to replace them, so contributors and users know where new work goes.

• README.md: new "Scope and frozen features" section.
  • HTML viewer (IfcHtmlViewerExporter, ifcio view): viewing moves to IOViewer through a planned IfcIO.Scene adapter over the planned shared IOScene model.
  • GLB and OBJ export (IfcGlbExporter, IfcObjExporter): a shared GLB writer is planned in IOScene.Formats.
  • Clash, measure, grids, diff and BCF (IfcClashDetector, IfcClashGrouper, IfcMeasureEngine, IfcGridSystem, IfcDiffEngine, BcfArchive, BcfZipExporter): planned to move to an IOCoord package.
  • IFC work-schedule (4D) sequence logic stays in IfcIO.
  • None of the replacement packages is published yet. Frozen features stay available and are removed no earlier than IfcIO 1.0, and only after a published replacement exists.
• CHANGELOG.md: one line under [Unreleased] / Changed pointing to the new README section.
• .github/dependabot.yml (new): weekly update checks for NuGet and GitHub Actions.

No source, API or package changes.

Tests

• Build and tests: not run (no code changes).
• dependabot.yml: not validated.
• README links: not checked beyond the IOViewer repository being public.

Notes

• Merge order: no dependencies. It touches no code and there are no other open IfcIO PRs, so it can merge on its own at any time.
• The Dependabot config is not documentation and has no CHANGELOG entry; it can be split into its own PR if preferred.
• Follow-up: when IfcIO.Scene, IOScene, IOScene.Formats or IOCoord is published, update the "None of these packages is published yet" sentence and link the package.