fix(ci): fix GNU sed syntax in Pdoc workflow and add manual trigger

[245678000000]

Fixes

Fixes: #316

Summary

The Pdoc workflow (.github/workflows/pdoc.yml) runs on ubuntu-latest (GNU sed), where sed -i '' causes sed to treat '' as an empty script and the following regex argument as a target filename, resulting in sed: can't read ...: No such file or directory.

This PR:

1. Removes the macOS-specific '' argument from sed -i so it executes properly under GNU sed.
2. Adds a workflow_dispatch: trigger to allow manually re-running the docs build workflow from GitHub Actions without re-pushing/moving release tags.
3. Updates CHANGES.md.

AI Disclosure

• No AI tools were used to create the content of this PR.
• Parts of this PR were created with the help of an AI tool, and I have carefully reviewed all of its content and take full responsibility for it.

[claude]

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[mlissner]

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Code review found no issues

No high-confidence issues detected in this change.