feat: converting documentation to mkdocs

[gvwilson]

Paired with plotly/plotly.js#7469 (formatting changes to JavaScript that Python docs are derived from).

• Move contents of commands.py to scripts in new bin directory and break
  into individual scripts.
  • Tidy up imports etc. while doing so.
• Move code generation from ./codegen to ./bin/codegen.
• Move plot-schema.json to ./resources rather than burying it under the
  codegen folder.
• Add Makefile to run commands instead of putting everything in commands.py.
  • Run ruff directly for checking and formatting rather than launching a
    subprocess from Python as commands.py did.
• Modify .gitignore to ignore docsanddocs_tmp. (Will eventually want to include docsor overwritedoc`.)
• Minor reformatting of README.md.
• Update CONTRIBUTING.md to describe relocation of commands and code
  generation to bin.
  • CONTRIBUTING.md documents --local, --devrepo and --devbranch options
    for updating JavaScript bundle that commands.py didn't seem to provide.
• Add mkdocs.yml configuration file for mkdocs.
  • Most of this file was vibe coded using Claude.
  • mkdocs does not support reading configuration from pyproject.toml, so
    we need the extra config file.
  • Use material theme.
  • Read hand-written Markdown from pages and write output to docs.
  • Generate module index pages on the fly using mkdocs-gen-files plugin.
    (See discussion of bin/generate_reference_pages.py below.)
  • Set docstring style to google (even though much of our documentation
    isn't formatted that way).
• Add placeholder Markdown files in pages that include files from the root
  directory (README, code of conduct, contributors' guide, license).
  • Remove relative links between these pages because they don't work when
    the content is transcluded one directory lower.
• Modify docstring in plotly/_subplots.py to escape closing ] with backslash
  to avoid confusing mkdocs Markdown.
  • Here and elsewhere the escape is written \\] because we need \] in the
    actual string. We could convert the docstrings to literal strings prefixed
    with r to avoid the double backslash.
  • Have also escaped some [ as \\[ for the same reason.
• Similar change to plotly/basedatatypes.py.
• Reformat line breaks in docstrings in plotly/express/_core.py.
• Modify pyproject.toml to install mkdocs and related packages for dev.
• Modify pyproject.toml to install pydoclint for checking documentation.
  • Currently reporting a lot of errors.
• Update uv.lock to match.

To do:

• Move scripts/gen_ref_pages.py into commands.py. (Can't do this because mkdocs.yml only accepts the name of the script, not parameters.)
• Include content from docstrings in hand-written Python code.
• Include content from docstrings in generated Python code.
• Include navigation links in left nav bar.
• Clean up warnings produced by mkdocs.
• Add linting for docstring style.
• Clean up (many) errors reported by pydoclint.
• Re-introduce links between .md files in root directory (taken out because they don't resolve when those files are transcluded from pages/*.md).
• Fix \[ formatting glitch in the following files (caused by replacing ][ with ]\[ to avoid Markdown thinking it's a reference link, but the text is inside back quotes):
  • plotly/graph_objs/histogram2dcontour/_contours/index.html
  • plotly/graph_objs/contour/_contours/index.html
  • plotly/graph_objs/contourcarpet/_contours/index.html
  • plotly/graph_objs/table/_header/index.html
  • plotly/graph_objs/table/_cells/index.html