Feature: RTF to Markdown Smart Paste

[iamkeeler]

This implements a new "Smart Paste" feature for converting copied Rich Text Formatting (RTF) back into Markdown.

• RTFToMarkdownConverter: A new parser that enumerates the NSAttributedString runs from NSPasteboard to detect traits like .bold, .italic, and monospaced code blocks. It applies the necessary **, *, or ` markdown wrappers. It also escapes any literal markdown-like characters inside the RTF string so they aren't double parsed on the next convert.
• MainViewModel: Now continuously monitors the .general pasteboard. If .rtf data is detected alongside the change count increment, it flags hasRTFInClipboard. It also provides a method pasteRTFAsMarkdown() to automatically perform the conversion and append it to the current editor.
• ContentView: Uses the new view model flag to display an inline "wand" banner whenever RTF is present on the clipboard. It provides two buttons: one to inject the markdown ("Paste as Markdown") and one to dismiss the notification.

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PR created automatically by Jules for task 14627918854698978184 started by @iamkeeler

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