Introducing support for PDF uploads and image improvements, and more

This version includes a number of improvements and fixes:

• [NEW] Support for PDF and image attachments has been added to the OpenRouter API service. All OpenRouter models support PDF attachments. Image attachments are supported for select models
• [NEW] Support for PDF attachments has been added for OpenAI and Gemini API services.
• [NEW] Shortcut Cmd+Shift+Delete to clear opened chat (thanks @boriselec)
• [Improvement] The image previews have been completely overhauled to use the native macOS Quick Preview with the Share, Gallery, and "Open in Preview" options
• [Improvement] The attached files are now saved as a draft until the message is sent
• [Improvement] Reasoning text is now collapsed by default
• [Improvement] Reasoning time is now displayed and saved
• [Fix] The bug that caused the sidebar with the chat list to automatically expand when a new chat was created has been fixed. It now only expands when the first chat is created
• Other minor fixes and improvements