update-core: major releases need Saddle's own setting, off by default #359

Problem

update-core (#351, merged in #357) applies a major WordPress release when WordPress's own "automatic updates for all new versions" switch is on. WordPress turns that switch on by default for every site installed since 5.6, so on most sites an app can apply a major release that the owner never chose to allow. That switch also answers a different question: what WordPress does unattended. An update through Saddle is attended (preview, then a confirm), like the "Update to version" button in Dashboard → Updates, which ignores that switch.

Fix (Fahim, 2026-10-13: "fix major release issue what best fit")

• A Saddle setting, Major WordPress releases, in Saddle → Settings → Updates. Off by default. Core settings are agent: read, and update-option only writes its allowlist, so no tool can turn it on.
• update-core applies a major release only when it is on, whatever WordPress's own switch says. Minor and security releases are unchanged.
• The runner checks it again when the run starts: an owner who turns it off after the confirm stops the update.
• Copy: the tool description, the refusal, the context line, readme, CLAUDE.md hard line, ROADMAP.

Ships in 1.5.2.