Drag and drop silently turns off with any filter, more than 100 issues or the archived view; the board's fallback move path is dead code

Part of PAR-357.

Problem

• List. Drag-to-reorder is only enabled with no filters, at most 100 issues, and outside the archived view (issues page.tsx:219). Nothing tells you why it stopped working.
• Board. draggable={allowOrder && …} (ui/.../board/BoardDnd.tsx:147) disables dragging between columns whenever any filter is active. That leaves the patchIssueAction fallback for unordered status moves (:98-100) unreachable. Filtering the board, which is the most common use, removes the core board interaction.
• Feedback. It shows as inline "Saving…" / "Saved." StateBlocks above the grid, which shift the layout.
• Keyboard and touch. DnD is HTML5 and mouse-only; there is no keyboard or touch support.

Do

• Always allow dragging between columns or groups (a status change). Only disable reordering within a group when the order is ambiguous, and show a hint on drag ("Manual order is off while filtered").
• Move to a DnD library with keyboard and touch sensors (e.g. dnd-kit).
• Show feedback as a toast; keep the optimistic update and rollback.