Work on documentation: Web-manuals

[willend]

Free-form text area

Please describe what your PR is adding in terms of features or bugfixes:

Adds html-based manuals. See #2664

Further fixes annoyance with the GRAMMAR docs in the current conda-release.

Details that still need work:

• Issue with e.g. scandinavian æøå / umlauted chars ü,ö,ä ✅
• Currently a tgz is dumped in the dockpg folder - should become part of doc-installdir / linked from mcdoc ✅

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Declaration of use of AI-tools

• Please add a checkmark here if you used AI-tools during the work for this contribution
• Furter, please describe how / where and for what the tools were used:

Lots of Claude-prompts, but focus on keeping to standard tools (tex4ht, CMake, python, js header injection)

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Development OS / boundary conditions

Please describe what OS you developed and tested your additions on, and if any special dependencies are required:

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PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution contains something else

  • Explanation is added in free form text above or below the checklist

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