feat: retry on rate_limit_exceeded errors

[devinscodebase]

When the Resend API returns a 429 with error name rate_limit_exceeded, the CLI now retries up to 3 times before giving up. It reads the retry-after header when available, falling back to exponential backoff (1s, 2s, 4s). The spinner updates to show retry status.

Only rate_limit_exceeded is retried. Quota errors (daily_quota_exceeded, monthly_quota_exceeded) are not retried since they will not resolve by waiting.

Closes #41

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Summary by cubic

Add automatic retries for 429 rate_limit_exceeded in CLI ops and show retry status in the spinner.

• New Features
  • Retries up to 3 times in withSpinner; uses retry-after when present, else 1s/2s/4s; derives MAX_RETRIES from delay list.
  • Skips retries for daily_quota_exceeded and monthly_quota_exceeded.
  • Tests cover retry-after parsing, fallback delays, and non-retryable errors; migrated to vitest; batch email test now uses application_error.

^{Written for commit bca3154. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

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