fix(error-reporting): silence ValidationError in classifySilenced

[sentry]

Previously, ValidationErrors, such as those arising from invalid user input for flags like --action-match in sentry alert issues create, were being reported to Sentry as issues.

These errors represent user input mistakes and should be silenced to prevent noise in Sentry. The root cause was that classifySilenced() in src/lib/error-reporting.ts did not explicitly handle ValidationError, causing it to fall through and be captured.

This change updates src/lib/error-reporting.ts to:

1. Add "validation_error" to the SilenceReason type.
2. Include a check in classifySilenced() to return "validation_error" when an instanceof ValidationError is encountered.

This ensures that ValidationErrors are now correctly silenced and tracked via the cli.error.silenced metric, rather than being sent as Sentry issues.

Fixes CLI-20M

_{Comment @sentry <feedback> on this PR to have Autofix iterate on the changes.}

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[sentry]

Bug: The change to silence ValidationError in classifySilenced will cause multiple existing tests to fail, as they expect these errors to be reported.
_{Severity: HIGH}

Suggested Fix

The tests that verify the behavior of ValidationError need to be updated to align with the new intention of silencing these errors. Either remove the ValidationError case from the test that expects it not to be silenced, or update the integration tests to no longer expect Sentry.withScope to be called for ValidationError. Alternatively, if ValidationError should not be silenced, revert this change.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: src/lib/error-reporting.ts#L95-L97

Potential issue: The modification in `classifySilenced` to handle `ValidationError` will
cause existing tests to fail. A unit test expects `classifySilenced(new
ValidationError(...))` to return `null`, but it will now return `"validation_error"`.
Additionally, several integration tests rely on `reportCliError` processing
`ValidationError` instances and invoking `Sentry.withScope`. Since the error is now
silenced, `reportCliError` will return early, and these tests, which expect Sentry scope
tags to be set, will fail because the test files were not updated to reflect this new
behavior.

Also affects:

• test/lib/error-reporting.test.ts:321~329

_{Did we get this right? 👍 / 👎 to inform future reviews.}