Handle command failures consistently without stack traces

[mthalman]

Some commands relied on System.CommandLine's default exception handler, which exposed full .NET stack traces for expected user errors such as unknown setting names.

Summary

• add a root invocation boundary that writes concise diagnostics to stderr and returns exit code 1
• preserve registry-specific error and authentication guidance
• retain silent process cancellation while treating unrelated cancellation exceptions as command failures
• cover invalid settings, cancellation paths, and representative registry failures

Testing

• dotnet test --no-restore -v minimal -c Release --filter "Category!=Integration" (984 passed across .NET 9 and .NET 10)
• focused command failure and cancellation tests (42 passed across .NET 9 and .NET 10)
• live-registry integration tests were not run locally because Docker was unavailable

Fixes: #313

[Copilot]

🟡 Changes recommended

Root-level OperationCanceledException handling currently suppresses diagnostics even when cancellation wasn’t actually requested, which can hide failure messages and conflicts with the stated behavior.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR standardizes command-failure handling at the CLI root invocation boundary so expected user errors (e.g., invalid settings names) no longer surface full .NET stack traces, while preserving existing registry-specific error messaging behavior.

Changes:

• Routes Program execution through a new CommandHelper.InvokeRootCommand wrapper that disables System.CommandLine’s default exception handler and emits concise diagnostics to stderr with exit code 1.
• Hardens error rendering in CommandHelper.WriteError to always restore console color via try/finally.
• Adds/extends tests covering concise failure output for invalid settings, representative registry failures, and cancellation behaviors.

File summaries

File	Description
src/Valleysoft.Dredge/Program.cs	Switches root invocation to a centralized wrapper for consistent error handling.
src/Valleysoft.Dredge/CommandHelper.cs	Introduces root invocation boundary and refines error output behavior.
src/Valleysoft.Dredge.Tests/RegistryIntegrationTests.cs	Asserts registry failures do not leak stack traces/type names.
src/Valleysoft.Dredge.Tests/CommandCancellationTests.cs	Adds coverage for root-level failures and cancellation scenarios.
src/Valleysoft.Dredge.Tests/CliProcessTests.cs	Adds end-to-end process test for invalid settings producing concise stderr.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Lite

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