v0.8.6 — Drag-to-reorder speaker cards (device-side, persistent)

• feat(ui): Speaker cards can be reordered by dragging the grip handle (⠿) in the card header. The order is persisted device-side via POST /api/speakers/order (SpeakerInventory::reorder reorders the speaker vector and saves to NVS), so it is identical across browsers and survives a reboot — no browser localStorage. Newly discovered speakers append at the end. Verified on S3: reorder, partial-order append of unnamed speakers, and reboot persistence. Addresses the speaker-sort request from issue #7 / the FHEM forum thread.

WebUI + firmware change — OTA-updatable from any earlier 0.8.x.