feat(linux): add network diagnostics provider

[LyCecilion]

Summary

• add and wire xidio.Platform.Linux into the CLI and solution
• collect Linux OS and privilege details, physical adapters, kernel drivers, MTU, and link state
• collect Wi-Fi details through iw and NetworkManager with graceful fallback
• collect DHCP leases, IPv4 and IPv6 routes, default routes, metrics, and neighbors through nmcli and iproute2
• add bounded cancellable external command execution
• update Nix tools, README, architecture, roadmap, and changelog
• remove unsupported x86_64-darwin devShell from current nixpkgs

Validation

• Fedora 44 real-host smoke test for wired and wireless adapters
• dotnet build xidio/xidio.CLI/xidio.CLI.csproj -c Release -f net10.0: 0 warnings, 0 errors
• nix flake check --no-build --all-systems path current checkout: all declared systems passed

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