docs(readme): drop the false CI claim from Requisite

[countzero]

Documentation only, a two-line deletion. switch_claude_account.ps1 is byte-identical to v4.2.0, so this carries no version bump, no changelog entry and no release, for the same reason as #22: tagging it would publish an asset nobody's copy differs from.

What changed

Removed "The test suite runs on all three on every push." from Installation → Requisite.

The claim is false. .github/workflows/tests.yml restricts its push trigger to main, so a push to develop runs nothing; CI fires on a pull request, on a push to main, and on workflow_dispatch. The v4.2.0 release pull request demonstrated the gap rather than hypothesizing it: it was the first run over 24 commits, and it failed two tests on both Unix legs that no Windows run could have caught.

Nothing replaces the line. It was reassurance sitting in an install section, and the badge row and the workflow file already answer the question for anyone who is asking it.

Shortcomings

• The workflow's trigger is unchanged, so the gap the line was papering over is still there. Deleting a false sentence makes the README honest; it does not make the branch tested.
• README prose remains untested by anything. This claim went stale silently and the next one will too.

Feedback I want

• Argue for fixing the trigger instead of the sentence. Adding develop to the push branches would make the original claim true and close the gap that let 24 untested commits reach a release pull request. I did not do it here because it is a CI change wearing a documentation change's clothes, and it belongs in its own pull request with its own argument about runner minutes.

What is not done

• No change to tests.yml. See above.
• No replacement sentence about CI coverage in Requisite, deliberately.