Port upstream safety and reliability fixes

[Rouniy]

Summary

• adapt the applicable safety and reliability changes from upstream PRs Preserve relative-alt guided behavior by setting Locationwp.frame at implicit callers ArduPilot/MissionPlanner#3728, Harden COM port enumeration to avoid Bluetooth-driven startup/dropdown crashes ArduPilot/MissionPlanner#3740, MAVFtp: Supports non-ASCII filenames in ListDirectory ArduPilot/MissionPlanner#3710, Fix HttpClient misuse: reuse static instance, remove duplicate headers, add missing error handling ArduPilot/MissionPlanner#3715, Use MAV_CMD_DO_CHANGE_ALTITUDE and MAV_CMD_DO_REPOSITION for moving vehicle ArduPilot/MissionPlanner#3724, Better camera/gimbal message rate handling ArduPilot/MissionPlanner#3679, Remove unnecessary COMMAND_ACK ArduPilot/MissionPlanner#3705, Proximity: Fix Proximity UI concurrency issue ArduPilot/MissionPlanner#3222, CaptureMJPEG: tolerate missing Content-Type / Content-Length in MJPEG; add boundary sniffing & lengthless frame reads ArduPilot/MissionPlanner#3603, gps base: fix Septentrio automatic configuration for RTK base station (port detection) ArduPilot/MissionPlanner#3752, Mavlink: update MAG_CAL_STATUS failure enums ArduPilot/MissionPlanner#3750/ConfigHWCompass: surface MAG_CAL_FAILED_OFFSETS / FAILED_DIAG_SCALING / FAILED_RESIDUALS_HIGH failure codes ArduPilot/MissionPlanner#3722, HUD/PrearmStatus: fix failure messages ArduPilot/MissionPlanner#3250 and Check ADS for zone identifier before trying to load a dll plugin. ArduPilot/MissionPlanner#3646 to the Avalonia/CoreCLR architecture
• fix confirmed upstream issues Downloading dataflash logfiles with Mission planner is very unreliable. ArduPilot/MissionPlanner#3461 (bounded range-aware DataFlash recovery) and MissionPlanner is deleting signing keys randomly ArduPilot/MissionPlanner#3694 (durable atomic MAVLink signing-key storage with safe legacy migration)
• remove the accidentally retained 117-file legacy MetaDataExtractorCSharp240d project after proving that active GeoRef/Survey paths use the maintained package
• document the issue disposition matrix, including rejected WinForms/Mono/GStreamer-only changes and the ArduPilot-owned ATC_HOVR_ROL_TRM Is giving out of range warning on heli when set to negative ArduPilot/MissionPlanner#3746 metadata correction

Validation

• Release solution build: 0 warnings, 0 errors
• full test suite: 1344 passed, 0 failed (two consecutive final runs)
• all port-source, WinForms retirement, project, binary, key and native-surface checks pass
• active NuGet graph reports no known vulnerable direct or transitive packages
• Linux TAR and DEB built locally; TAR/dpkg integrity and lintian pass
• extracted DEB reaches the normal Avalonia loop under Xvfb for the 12-second smoke window

Review notes

The commits are intentionally atomic. Proposed upstream patches were not cherry-picked blindly: each was compared with the current port, strengthened where needed and covered by focused tests. CI should validate Linux TAR/DEB, Windows ZIP/MSI and macOS x64/arm64 ZIP/DMG on native runners; CodeQL must pass before merge.