On-demand position update: AdminMessage.request_position_update (protobufs#1032)

[jamesarich]

Tracks the Android side of meshtastic/protobufs#1032 (open). Firmware meshtastic/firmware#11403 and web meshtastic/web#1028 exist; Android has nothing.

Schema: AdminMessage.request_position_update = 70 (bool) — asks the node for an immediate GPS sampling cycle; firmware coalesces repeats within 10 s.

• blocked on protobufs#1032 merge + protobufs bump
• CommandSenderImpl: send to local or remote node
• node detail / map: "Update position now" action next to the existing position request, debounced ≥10 s to match firmware