Migrate to System.CommandLine 2.0.x stable (InvocationConfiguration API)

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Context

Dependabot PR #31 bumped System.CommandLine from
2.0.0-beta5.25306.1 to 2.0.8. The stable 2.0 API drops the
beta-era ParseResult.InvokeAsync(CancellationToken) overload in
favour of an InvocationConfiguration shape that the beta did
not have. Held at the beta in commit 9bada36 to keep the build
green.

Affected files

• src/IviCli.Cli/Program.cs (return await root.Parse(args).InvokeAsync(cts.Token);)
• Likely every subcommand SetAction callback signature, depending
  on whether the new API changes the lambda shape.

Acceptance

• System.CommandLine pinned at the current stable.
• Program.cs builds cleanly and the root + every subcommand still
  pick up CancellationToken from the runtime.
• All CLI tests stay green.