fix: don't treat 429 as success in sendToRelay

[SirBrenton]

What

sendToRelay in lib/reporter.js was returning true when the relay responded with 429, treating a rate-limited request as accepted.

// Before
return resp.ok || resp.status === 429; // rate-limited is fine, not an error

// After
return resp.ok; // 429 returns false — let callers decide whether to retry

Why this matters

A 429 means the relay did not accept the report. Returning true silently dropped crash reports under sustained rate limiting — giving callers false confidence that reporting succeeded when data was lost.

Fix shape

Return false on 429. Preserves the never-throws contract. No blocking retry logic added. Callers decide whether to retry.