feat: add bookmarks command

Add `bird bookmarks` command to fetch the authenticated user's bookmarked tweets.

- New `getBookmarks()` method in TwitterClient
- Uses graphql_timeline_v2_bookmark_timeline feature flag
- Supports `--count` and `--json` options
- Follows existing patterns for query ID rotation and retry logic

Usage:
  bird bookmarks           # Get your recent bookmarks
  bird bookmarks -n 50     # Get 50 bookmarks
  bird bookmarks --json    # Output as JSON

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

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

src/index.ts

@@ -138,6 +138,7 @@ const KNOWN_COMMANDS = new Set([
   'thread',
   'search',
   'mentions',
+  'bookmarks',
   'help',
   'whoami',
   'check',
@@ -310,6 +311,7 @@ program
       'TweetDetail',
       'SearchTimeline',
       'UserArticlesTweets',
+      'Bookmarks',
     ];
 
     if (cmdOpts.fresh) {
@@ -671,6 +673,39 @@ program
     }
   });
 
+// Bookmarks command - get user's bookmarks
+program
+  .command('bookmarks')
+  .description('Get your bookmarked tweets')
+  .option('-n, --count <number>', 'Number of bookmarks to fetch', '20')
+  .option('--json', 'Output as JSON')
+  .action(async (cmdOpts: { count?: string; json?: boolean }) => {
+    const opts = program.opts();
+    const timeoutMs = resolveTimeoutFromOptions(opts);
+    const count = Number.parseInt(cmdOpts.count || '20', 10);
+
+    const { cookies, warnings } = await resolveCredentialsFromOptions(opts);
+
+    for (const warning of warnings) {
+      console.error(`${p('warn')}${warning}`);
+    }
+
+    if (!cookies.authToken || !cookies.ct0) {
+      console.error(`${p('err')}Missing required credentials`);
+      process.exit(1);
+    }
+
+    const client = new TwitterClient({ cookies, timeoutMs });
+    const result = await client.getBookmarks(count);
+
+    if (result.success && result.tweets) {
+      printTweets(result.tweets, { json: cmdOpts.json, emptyMessage: 'No bookmarks found.' });
+    } else {
+      console.error(`${p('err')}Failed to fetch bookmarks: ${result.error}`);
+      process.exit(1);
+    }
+  });
+
 // Whoami command - show the logged-in account
 program
   .command('whoami')