📚 Document spaces in inventory object names

[sapunyangkut]

Summary

• document that spaces in inventory object names must be percent-encoded as %20 in inv autolinks
• add the required Unreleased documentation changelog entry

Validation

• git diff --check
• exact source checks for the encoded autolink, decoded inventory target, changelog placement, and non-overlap with [ENH/FIX] Support headings in nested parse #1102
• pre-commit and tox -e docs-clean were unavailable in this environment

Closes #991.

Disclosure

This pull request was prepared with AI-assisted automation under explicit human authorization. The validation limitations are disclosed above.