Adds a `filterSelfMentions` method to `MentionBot.swift` that uses `NSRegularExpression` to strip case-insensitive bot username mentions from AI responses before posting, preventing infinite reply loops. Updates the default OpenRouter model from `x-ai/grok-3-fast-beta` to `x-ai/grok-code-fast-1` in README.md, along with revised example model identifiers for Claude, Gemini, and other providers.