feat: add image upload support for post/reply/quote commands

- Add upload_media() method to TwitterClient (INIT/APPEND/FINALIZE flow
  via upload.twitter.com, supports JPEG/PNG/GIF/WebP up to 5MB)
- Extend create_tweet() and quote_tweet() with optional media_ids param
- Add --image/-i option to post, reply, and quote CLI commands (max 4)
- Add MediaUploadError exception for upload-specific error handling
- Add 6 unit tests covering upload flow, validation, and media_ids

Co-Authored-By: Catafal <67582323+Catafal@users.noreply.github.com>

twitter_cli/exceptions.py

@@ -36,6 +36,10 @@ class QueryIdError(TwitterError):
     """Raised when a GraphQL queryId cannot be resolved."""
 
 
+class MediaUploadError(TwitterError):
+    """Raised when media upload fails (file not found, too large, unsupported format, API error)."""
+
+
 class TwitterAPIError(TwitterError):
     """Raised on non-OK Twitter API responses with HTTP status + message."""