Docs: reduce duplicate indexing noise and preserve API pages

[jaelliot]

Summary

Docs configuration/indexing cleanup to reduce duplicate object noise while preserving content visibility.

Files

• README.md
• docs/source/conf.py
• docs/source/hio.core.rst
• docs/source/hio.core.serial.rst
• docs/source/hio.core.tcp.rst
• docs/source/hio.core.udp.rst
• docs/source/hio.demo.rst
• docs/source/hio.help.rst
• docs/source/hio.rst

Scope

• Conservative docs config/page indexing adjustments
• No runtime code changes

Validation

• Sphinx docs build clean

[jaelliot]

Leaving this PR open intentionally so Sam can see the work and close it himself if desired. The current aggregate review target is #154, which subsumes this docs indexing/config cleanup as part of the consolidated HIO docs/docstring cleanup pass.