Add OverlayParameters.multibeam_enabled

[jp-pino]

Adds bool multibeam_enabled = 25 to OverlayParameters so the app can toggle whether the multibeam sonar fan overlay is drawn onto recordings. Split out of #278 so the recorded-fan overlay can land separately from the color filter / RTSP work.

Linked PRs (multibeam overlay on recordings)

1. BluEye-Robotics/ProtocolDefinitions — this PR
2. BluEye-Robotics/p2_msgs#54 — OverlayParameters.msg mirror
3. BluEye-Robotics/p2_drone#1066 — mapping_overlay_parameters.cpp
4. BluEye-Robotics/gst_rtsp_record#297 — mbezoverlay in the record pipeline, gated by this flag

Flow: app → OverlayParameters.multibeam_enabled → node_comm → OverlayNode republishes on /overlay/get_parameters (tyndall) → UltraRecordApp reads it at record start and inserts mbezoverlay. Default false: nothing changes for apps that never set it.

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https://claude.ai/code/session_01VPvg8dPeNaaExzg3iCnzCF