Fix upstream issue audit round three

[Rouniy]

Summary

• fix confirmed upstream safety and correctness reports for parachute release, planner radii, parameter precision/encoding/comparison, mission-command input, SBS squawk retention and DataFlash parameter history
• adapt the applicable DroneCAN validation from upstream PR UAVCAN parameter editor now does min/max checking on numerical parame… ArduPilot/MissionPlanner#2644 and Pixhawk 6C driver entries from PR Drivers: add Holybro Pixhawk 6C USB ID (VID_3162 PID_0053) ArduPilot/MissionPlanner#3735
• synchronize the newer GTU NV5 unlocked-channel RSSI semantics from clean checkpoint f196ea689
• document audited upstream items that are already fixed or cannot be changed safely without their unavailable logs

Local verification

• dotnet build MissionPlanner.slnx -c Release --no-restore --nologo: 0 warnings, 0 errors
• complete Avalonia tests: 1400/1400 passed
• all six porting/inventory checks passed: 708/708 pinned paths, 1623 native rows, 0 blockers
• all 28 active projects: no known vulnerable direct or transitive NuGet package
• clean Linux TAR and DEB built
• lintian: no diagnostics
• extracted DEB payload assertions and 12-second Xvfb smoke passed

Release gate

Do not tag or publish a release from this branch. Merge only after the full Linux/Windows/macOS package matrix and CodeQL pass, then repeat and verify the same gates on the resulting master merge commit before creating the release.