docs: explain phase-shifting transformers with GenericBranch

[nightcityblade]

Fixes #1484

Summary

• document how generic_branch parameters map to a static phase-shifting transformer
• include a finite-reactance lossless example
• warn that an impedance-free ideal phase link is singular in the branch model

Testing

• PATH=/Users/shensheng/.nvm/versions/node/v24.18.0/bin:$PATH uv run --frozen --group lint pre-commit run markdownlint --files docs/user_manual/components.md
• git diff --check

The full Sphinx build could not reach the changed page locally because the generated Doxygen XML (docs/doxygen/build/xml/index.xml) is absent and Doxygen is not installed in this environment.

[mgovers]

Hi @nightcityblade,

Thank you for your contribution! I only have one minor comment. After you've resolved that, I will kick off CI.

[mgovers]

Hi @nightcityblade,

Thank you for the edit. The code looks good but I see that you do not have verified commits set up (see also https://power-grid-model.readthedocs.io/en/stable/contribution/CONTRIBUTING.html#commit-signature-verification). After you have done that (your commit should have a verified badge next to it) then this is good to go

[nightcityblade]

Thanks for catching the signature requirement. The requested documentation move is complete and the content checks pass; the remaining blocker is replacing the branch commit with a cryptographically signed commit that GitHub marks Verified.

[TonyXiang8787]

Hi @nightcityblade,

Thanks for your effort. For signed commits, you need to rebase your branch with signed (GPG or SSH) commits, then force push to this PR.

[scud-soptim]

I added also a PR for this Request

[TonyXiang8787]

Hi @nightcityblade,

I see you have closed this PR. Do you still intend to contribute the changes?

[nightcityblade]

Thanks for the guidance. I rewrote the branch with GitHub-verified signed commit c7e9b5f. It has the exact same Git tree as the previously tested commit, so the documentation content is unchanged; CI has been retriggered.

[mgovers]

Hi @nightcityblade,

This PR looks good. Thank you for the contribution!

Note that #1491 was also created to document the PST, but since this PR was first and in a good state, we give this one precedence. After this is merged, these docs can be extended with contents from the other PR, but that is out of scope of this PR.

Sent to merge queue 👍