feat: add cursor-based pagination for following/followers commands

Add pagination support to `bird following` and `bird followers` commands,
similar to existing pagination in search/bookmarks/likes.

Changes:
- Add `cursor` parameter to `getFollowing()` and `getFollowers()` client methods
- Return `nextCursor` in `FollowingResult` for pagination continuation
- Add `--cursor <cursor>` CLI option for manual pagination
- Add `--all` CLI flag to automatically fetch all pages
- Add `--max-pages <number>` option to limit pages when using --all
- Add input validation for --max-pages (requires --all or --cursor)
- Add deduplication using Set to prevent duplicate users
- Add 1-second delay between pages to avoid overwhelming the API
- Update `-n/--count` description to clarify it's per-page
- Add unit tests for cursor parameter and nextCursor response

Usage examples:
  # Fetch first page (default 20 users)
  bird following

  # Fetch with specific page size
  bird following -n 50

  # Use cursor for next page
  bird following --cursor "CURSOR_FROM_PREVIOUS"

  # Fetch ALL following users automatically (with rate limiting)
  bird following --all --json

  # Limit to first 5 pages
  bird following --all --max-pages 5

  # Same options work for followers
  bird followers --all

Note: REST API fallback does not support cursor pagination.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

src/lib/twitter-client-types.ts

@@ -280,6 +280,8 @@ export interface FollowingResult {
   success: boolean;
   users?: TwitterUser[];
   error?: string;
+  /** Cursor for fetching the next page of results */
+  nextCursor?: string;
 }
 
 export interface TwitterClientOptions {