feat(worksheets): select several rows and drag them together

[Artmann]

The sidebar could only ever move one worksheet at a time. Now several rows can be picked out and dragged as a group.

What you can do

• ⌘/Ctrl-click toggles a row in and out of the selection.
• Shift-click takes the range from the anchor, and re-measures from that same anchor on the next shift-click instead of growing one click at a time.
• Drag any selected row and all of them travel. A non-contiguous selection gathers into a block at the drop point, keeping its list order; every travelling row dims, since nothing here renders a drag preview.
• Right-click a selected row for "Delete 3 worksheets" behind one confirmation. Rename is dropped while it means nothing, the "never empty the list" guard still applies, and a half-failed delete reports Failed to delete 1 of 2 worksheets rather than stranding the rest.

A plain click still just opens one worksheet, and typing in the filter clears the selection — a filtered list cannot be dragged, and hidden rows should not be deletable.

Two decisions worth reviewing

The open worksheet is the implicit selection. With nothing picked out, a ⌘-click adds to the row you were already on rather than replacing it, so the first modified click cannot silently drop it. That fallback depends on view state the reducer does not have, so the slice is a holder (worksheetSelectionChanged) and the math runs at the call site — the same shape worksheetRenameStarted already uses.

Modified clicks do not open anything. Picking rows out to move them should not swap the editor under you.

Shape

• src/app/list-move.ts — moveIds, the block move. Returns the list it was given, by reference, for every drop that means nothing (row gone mid-drag, drop inside the moving block), which is how the hook knows to skip the write.
• src/app/list-selection.ts — toggle / extend / prune, all pure.
• src/app/hooks/use-list-reorder.ts — takes selectedIds as an option and adds isMoving. Single-row drags route through the same moveIds, so the tab strip and the database explorer are untouched.
• src/app/hooks/use-worksheet-selection.ts — prunes rows that have gone and applies the open-worksheet fallback.

Verification

Unit tests for both pure modules, multi-drag and isMoving cases in use-list-reorder.test.ts, and explorer tests for ⌘-click, Ctrl-click, shift-click, plain click, multi-delete, the all-selected guard, and the partial-failure message. Full suite green (1414 tests), typecheck and prettier clean.

Also driven against the running app, since jsdom cannot do a real drag: ⌘-clicked three non-contiguous rows, dragged them to the top of the list, and confirmed PUT /worksheets/order wrote them as a contiguous block in list order; shift-click ranges and the "Delete 3 worksheets" menu both behave in a real browser, where Radix menus have misled this project's jsdom tests before.

Deliberately not included

• No keyboard shortcut for delete — Backspace would fire inside the SQL editor.
• No ARIA selection semantics. Rows carry data-selected for styling and tests; making the list a real listbox would imply arrow-key navigation it does not have.

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit a0acbc5.}