fix(error-reporting): Silence ValidationError as user input error (CLI-1FN)

[sentry]

Previously, ValidationError instances were not explicitly handled by the classifySilenced function in packages/cli/src/lib/error-reporting.ts. This meant that user input errors, such as providing a non-existent directory to a sourcemap command, were being reported to Sentry as crashes rather than being silenced as expected user-facing errors.

This change addresses the issue by:

1. Adding 'user_input_error' to the SilenceReason type.
2. Introducing a new branch in classifySilenced to return 'user_input_error' when the error is an instance of ValidationError.

This ensures that ValidationErrors are now correctly silenced, preventing them from polluting Sentry crash reports while still allowing their volume to be tracked via the cli.error.silenced metric.

Related unit tests in test/lib/error-reporting.test.ts have been updated to reflect this new behavior, asserting that ValidationErrors are now silenced rather than captured.

Fixes CLI-1FN