Check removed HTML IDs

[encukou]

As discussed in https://discuss.python.org/t/tracking-removed-html-ids/106037, let's track HTML IDs in docs so that removing one is a conscious decision.

Linked PRs

• GH-145000: Add a tool to check removed HTML IDs #145001
• [3.14] GH-145000: Add a tool to record/check removed HTML IDs (GH-145001) #145212
• gh-145000: Run check-html-ids.py in CI #145632