Re-plan a limb lands from pull #2561's branch, with sealed titles tested, a bounded query and the refusal for non-admins #2585

Replaces #761. Pull #2561 is stuck after three change requests. Start from its branch scout/761-hand-a-limb-to-the-planner-to-re-plan-as rebased on main, and open a new pull.

Done looks like:

• [ ] test/limb-replan.test.ts asserts that a reader and a guest never see a sealed report's title on the milestone page, so the test fails if the sealed filter is removed.
• [ ] The hand-over query pushes taken_back_at IS NULL into SQL and is bounded by the last finished planning run, with no per-row answered query.
• [ ] A viewer who cannot administer the repository sees the refusal in place of the primary button, as blocked does.
• [ ] '1 issue' uses plural.