docs: generate yaml reference from pydantic

[frodehk]

Auto-generate a single-page YAML reference doc from the Pydantic models, so documentation stays in sync with the code.

Adds a new package scripts/yaml_reference_docs/ with this pipeline:

Pydantic models → KeywordNode tree → PageDoc → Markdown (index.md)

Module	Responsibility
keyword_tree.py	Traverse the Pydantic model hierarchy and build a tree of YAML keywords
introspect.py	Extract type labels, default values, and child models from Pydantic fields
doc_model.py	Dataclasses for the intermediate document model (PageDoc, SectionDoc, ItemDoc)
page_builder.py	Convert the keyword tree into a PageDoc ready for rendering
render_markdown.py	Render a PageDoc to Markdown for Docusaurus
example_builder.py	Generate YAML snippet examples
mdx.py	Escape text that would break MDX parsing (e.g. <YYYY-MM-DD>)
generate.py	CLI entry point — runs the full pipeline and writes index.md

The generator relies on Field(title="KEYWORD") to discover YAML keywords. Several existing model fields were missing title, so this PR adds Field(title=...) where needed. This has no runtime effect — it only adds metadata that Pydantic already supports.

The generated page appears under About → YAML Overview in the sidebar.

How to review

git checkout docs/generate-yaml-reference-from-pydantic

# Re-generate (optional — index.md is already committed)
python -m scripts.yaml_reference_docs

# Preview in Docusaurus
cd docs
npm install
npm run start

Then navigate to YAML Overview in the sidebar.

Refs:
equinor/ecalc-internal#1613

---

Type of Work

• Patch: X.Y.Z+1. NEGLIGIBLE visible changes, does not change input or output - OR changes behaviour. Use chore:, refactor: etc
• Minor: X.Y+1.Z. Minor changes, might ADD new input (YAML), or other backwards-compatible changes. Use feat:, fix:
• Major: X+1.Y.Z. Major and most likely BREAKING changes, wo. backwards compatibility, or removing temporary backwards compatibility functionality. Use ! or BREAKING:.

See here (internal): https://github.com/equinor/ecalc-internal/discussions/1044

Have you remembered and considered?

• IF FEAT: I have remembered to update documentation
• IF FIX OR FEAT: I have remembered to update manual changelog (docs/drafts/next.draft.md)
• IF BREAKING: I have remembered to update migration guide (docs/docs/migration_guides/)
• IF BREAKING: I have committed with BREAKING: in footer or ! in header
• I have added tests (if not, comment why)
• I have used conventional commits syntax (if you squash, make sure that conventional commit is used)
• I have included the Github issue nr in the footer!

What is this PR all about?

What else did you consider?

Between the lines?