Retry with exponential backoff on HTTP 429 (rate limiting)

[sujito00]

Problem

When X returns HTTP 429 (rate limited), all methods immediately fail and return an error. Users must manually re-run commands.

This is especially painful during pagination operations (search --all, bookmarks --all) where partial progress is lost.

Proposed solution

Add automatic retry with exponential backoff:

• Detect 429 responses in fetchWithTimeout or a wrapper
• Retry up to N times (default: 3) with exponential delay (1s, 2s, 4s)
• Respect Retry-After header if present
• Make max retries configurable via constructor option

const client = new XReaderClient({
  cookies: { ... },
  maxRetries: 3,    // default: 3
  retryDelay: 1000, // base delay in ms
});

Additional context

The paginated methods already have hardcoded sleeps (1000ms for search, 500ms for bookmarks), but these are preventive, not reactive. Both approaches should coexist.