feat: English translation, background notifications, and smart input features

[digvijay-ship-it]

This pull request localizes the userscript to English and integrates several smart input features:

• Full English Translation: Translated all comments, UI fallbacks, tooltips, dialogs, and notices. Used Unicode escape sequences on Chinese DOM selectors to keep the source file 100% free of Chinese character literals while maintaining Chinese interface compatibility at runtime.
• Flashing Tab Title Alerts: Added flashing document title alerts when a response completes while the tab is in the background, triggering a browser taskbar highlight.
• Smart Enter & Queue on Upload: Keydown events for Enter are intercepted and queued if attachments are uploading, submitting automatically once finished.
• Aggressive Paste Focus: Solved focus loss after pasting images by aggressively focusing the textarea input for 1 second.
• Scroll Button & Disclaimer Hider: Added setting controls and styles for a floating scroll-to-bottom button and hiding the footer disclaimer text.