KTailctl v0.16.0

Changes

• Cleanup the buttons in the peer list a bit
• Test building on LLVM 18
• Integrate CodeQL checking
• Integrate flawfinder
• Integrate cppcheck
• Add a nix flake

Bugfixes

• Some fixes according to clang-tidy
• Fix go get dirs for renovate integration

Chores

• Upgrade to KDE frameworks 6 and Qt6
• Update to go v1.22.1
• Update tailscale.com module to v1.62.0
• Update golang.org/x/net module to v0.22.0
• Update google.golang.org/protobuf to 1.33.0
• Update cachix/install-nix-action to v26