v0.9.0

Add global --no-mentions flag for all message sending commands

- Define _NO_MENTIONS_OPT as a global option for consistent usage
- Add --no-mentions flag to send, reply, thread-start, thread-reply, and edit commands
- Skip mention parsing entirely when flag is set to avoid breaking YAML/code content
- Add test for the --no-mentions functionality

This allows sending code, configuration files, and other content containing @ symbols
without them being incorrectly parsed as Matrix user mentions.