[JarryShaw]

• Searched for similar pull requests
• Followed the coding style (make pylint, make mypy, make isort)
• make test passes, and a test case covers the change
• Added a changelog entry — N/A, centralised in chore(docs): centralise changelog entries for unreleased versions #2483

What is the purpose of your pull request?

• fix — corrects a defect
• feat — adds a feature
• perf — changes performance, not behaviour
• refactor — changes neither behaviour nor performance
• test — tests only
• docs — documentation only
• ci — workflows or build tooling
• release — bumps the version or rolls up a distribution
• chore — anything else
• const — regenerates constant or registry tables, members keeping their numeric values

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Description of your pull request and other information

Follow-up to #2518 (#2512): pre-existing IGMP doc drift that its cross-review found.

• The IGMP.alias docstring and igmp.rst now match the code: IGMPv1 reports IGMP, not IGMPv1.
• IGMPv3 is added to the Mermaid graph in protocols/index.rst, with its click target, and to ext.rst's IGMP family rows.
• igmp.rst gains automethod:: id, so the conventions page's IGMP.id() reference resolves, and version now links.
• pep.rst no longer lists IGMPv3 (feat(internet): implement IGMPv3 (group-record list) #2448) as pending.

A Sphinx -E build against the pinned docs requirements shows no new warnings. The doc-claims, internal-refs, roles, ambiguous-xref and docstring-contract tests pass.

[JarryShaw]

Cross-review (Sonnet) at 282e427b7: GOOD TO GO. Each IGMP class's runtime alias matches the new text (IGMPv1 IGMP, v2 IGMPv2, v3 IGMPv3), and the igmp.py change is docstring-only by AST comparison. In a pinned-requirements Sphinx build, every Mermaid click target resolves, ext.rst's IGMP family spans all four rows, and every IGMP cross-reference on the conventions page links, including IGMP.id(). The six doc and IGMP test modules pass. Unverified: how the Mermaid graph renders in a browser.