v1.5.10 — T-309 complete: drag-to-reorder mit slots

Added — interactive drag on the strat editor's mit-window overlay

• The v1.5.8 SVG bars in MitWindowOverlay (web/src/StratEditor.jsx) are now draggable. Grab a bar with the mouse, slide it horizontally — window_offset_ms updates live and the form row above updates too (they're bound to the same slots state).
• Snap to 500 ms — matches the existing <input step={500}> granularity on the form's window-offset cell, so dragging and typing produce the same set of representable values.
• Constrained to visible domain — a bar can't be dragged past the overlay's time bounds. Right-edge clamps at maxT - duration; left edge at minT.
• Visual feedback — dragging bar gets a blue stroke + higher opacity; cursor flips from grab to grabbing; the bar's text label appends (t+5.5s) showing the live offset.
• Pointer capture — uses setPointerCapture so the drag survives the cursor leaving the bar (no stuck drags if you slide too far).
• No new tests — pure UI interaction; covered by manual smoke. The state update (setSlots[i].window_offset_ms) is the same path tests already exercise via the form input.

T-309 status

Both halves of T-309 are now shipped:

• v1.5.8 — click-to-add mit palette + visual window overlay with role colors and overlap-by-construction.
• v1.5.10 — drag-to-reorder. Form row still works for keyboard editing / precise values.

PLAN §11 T-309 is complete. IDEAS.md entry collapsed accordingly.