Regenerate class diagrams from source and fix contribution guides

[daniel-locatelli]

Summary

Fixes the four pre-existing class diagrams (Elements, Connections, Fabrication, Errors) so they match the actual v2.2.0 code, and makes them reproducible:

• The diagrams are generated with a pipeline maintained outside this repo at https://github.com/daniel-locatelli/compas_timber-class-diagrams: class bodies, inheritance and attributes are extracted from src/ with Python's ast (ground truth), while subsystem partitioning, prose and cross-class edges are curated in diagram_spec.py. Curated composition edges are asserted against the extracted attributes so they fail loudly when the code changes; see that repo's README for usage.
• Regenerates docs/contribution/class_diagrams.md from that pipeline; the page header now states it is generated and must not be edited by hand.
• Drops the Data base-class nodes (they carried no discriminating information — the prose states the convention and its exceptions instead).
• Draws the constants classes (OrientationType, StepShapeType, TenonShapeType, AlignmentType, EdgePositionType, LimitationTopType) and MachiningLimits as explicit blocks with source-verified usage edges — previously the constants classes appeared in the diagrams only as attribute types, and MachiningLimits not at all. BTLxFromGeometryDefinition gains an instantiates edge to BTLxProcessing in place of the dropped Data link.
• Per review: CutPlaneSpec / MiterPlaneSpec are left out of the Connections diagram while that mechanism is reworked in Add BTLx UserReferencePlane support, remove CutPlaneSpec/MiterPlaneSpec #803, and the Fabrication intro links the BTLx standard specification.
• Fixes broken mermaid rendering on the published site via mkdocs.yml: the superfence formatter is switched from mermaid2's non-escaping fence_mermaid_custom to pymdownx.superfences.fence_code_format, because the non-escaping variant let the browser parse class-diagram stereotypes like <<abstract>> as HTML tags and render them as empty <>. (The panzoom enablement originally bundled here landed separately via Make mermaid class diagrams zoomable in docs #788; this branch has been rebased onto main accordingly.)
• Rewrites the joints contribution guide to match the v2.2.0 Joint base-class API: corrects the JointTopology values (the old page misdescribed TOPO-X/TOPO-I and was missing TOPO_Y, TOPO_K and the plate topologies), replaces the outdated elements / restore_beams_from_keys() requirements with the automatic GUID restoration and the _set_unset_attributes() hook, documents check_elements_compatibility() as a classmethod, and makes the add_features example idempotent on re-run. This API is unchanged on current main, so the guide stays correct after the merge; the one thing to revisit for the next release is the example's manual remove-features-first step, which post-2.2.0 code supersedes with the new Joint.clear_features().

Docs-only change, no CHANGELOG entry ("no changelog" label).

Heads-up: post-2.2.0 hand-edits to the diagrams are superseded

main received hand-edits to class_diagrams.md documenting post-2.2.0 additions (e.g. CompositeJoint from the composite-joint work). This PR replaces the page with the generated 2.2.0 snapshot, so those entries are intentionally not included — the diagrams document the released version, and new classes will re-enter the diagrams when they are regenerated for the next release (the compare script in the pipeline repo reports any unplaced classes). Going forward the page should not be edited by hand; the header now says so.

Note for maintainers: updating the published 2.2.0 docs

The docs workflow only deploys the mkdocs site on version tags, so merging this PR does not update the live site by itself — the fixes would first appear with the next release tag. If we want the published "2.2.0 (latest)" docs to show the corrected diagrams before then, someone with push rights needs to run, from the merged main:

mike deploy 2.2.0 latest --push

This rewrites only the 2.2.0 folder on gh-pages (no git tag is created or moved).

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.64%. Comparing base (85bc4b6) to head (86cbd8d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #812      +/-   ##
==========================================
- Coverage   82.67%   82.64%   -0.04%     
==========================================
  Files          83       83              
  Lines       12005    12005              
==========================================
- Hits         9925     9921       -4     
- Misses       2080     2084       +4     

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[chenkasirer]

mmh dunno if this suite of scripts should end up as part of compas timber. if it can be generalized, perhaps it's worth packaging this as some kind of a developer tool. otherwise, I would just remove it from here.

[daniel-locatelli]

Agree, I removed the scripts and have them here. I've been thinking about how to keep the diagrams from drifting long-term. Ideally they would be generated as part of the docs CI. If you think that makes sense I can write it as an issue.