fix(error-reporting): Silence ValidationError

[sentry]

Currently, ValidationErrors, which typically indicate malformed user input (e.g., invalid JSON for --condition flags), are not explicitly silenced in the CLI's error reporting mechanism. This leads to these user-facing errors being captured and sent to Sentry as if they were internal bugs.

This PR addresses the issue by:

• Adding "validation_error" to the SilenceReason type in src/lib/error-reporting.ts.
• Modifying classifySilenced() to recognize ValidationError and return "validation_error", thereby preventing these errors from being reported to Sentry.

This ensures that Sentry reports are focused on actual CLI defects, while user input errors are handled gracefully without generating unnecessary Sentry events.

Fixes CLI-1ZD

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

[github-actions]

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[sentry]

Bug: The change silences all ValidationError instances, but some are used for internal logic errors (like exhaustiveness checks), not just user input. This will hide CLI bugs from Sentry.
_{Severity: MEDIUM}

Suggested Fix

Instead of silencing the entire ValidationError class, the silencing logic should be more specific. Consider silencing only ValidationError instances that are known to be from user input, perhaps by checking for a specific field or message pattern, or by only silencing them when thrown from specific validation functions. This would allow internal errors to still be captured.

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#L106-L108

Potential issue: The change in `classifySilenced` now silences all `ValidationError`
instances. However, the codebase uses `ValidationError` not only for user input errors
but also for internal CLI defects. For example, exhaustiveness checks in
`src/lib/trace-target.ts` throw `ValidationError` to catch unhandled cases in
discriminated unions. Silencing these errors means that genuine bugs in the CLI's logic
will no longer be reported to Sentry, hindering debugging and maintenance. An existing
test explicitly asserts that `ValidationError` should not be silenced, which will fail
with this change.

Also affects:

• src/lib/trace-target.ts
• src/commands/trial/start.ts

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