Align local docs builds with Read the Docs apidoc

[acul71]

Summary

• Fixes Fix Read the Docs build failures #31
• Updates Makefile docs-ci and build-docs to use python -m sphinx.ext.apidoc -o docs/ multibase, matching .readthedocs.yaml pre_build
• Documents the local docs build command in CONTRIBUTING.rst

Note: Sphinx source_suffix / root_doc and RTD pre_build were already fixed on master; this PR closes the remaining local/RTD drift.

Demo / evidence

$ make docs-ci
python -m sphinx.ext.apidoc -o docs/ multibase
...
build succeeded.

Explanation: Local CI now invokes the same module-path apidoc command as Read the Docs, with warnings as errors (SPHINXOPTS=-W). Exit code 0.

Test plan

• make lint
• make typecheck
• make test
• make docs-ci (exit 0, -W)

Made with Cursor

[acul71]

Demo logs (docs-ci)

$ make docs-ci
python -m sphinx.ext.apidoc -o docs/ multibase
...
build succeeded.

Local docs now use the same python -m sphinx.ext.apidoc path as Read the Docs pre_build, with -W (warnings as errors). Exit code 0.

[acul71]

@sumanjeet0012 Could you please review this PR when you have a chance? Thanks!