iOS: Add “Copy raw text” action for linked files

Feature request

On iOS, linked files currently expose actions like Preview, Source, and Copy path. It would be very useful to also have a simple Copy raw text action.

The key behavior is that this should copy the file's actual source contents, not the rendered preview text.

For example, for a Markdown file, copying raw text should preserve Markdown syntax such as:

# Heading

- item
- **bold**
- `code`

[link](https://example.com)

rather than copying only the visually rendered text.

This would make it much easier to move file contents from T3 Code on iOS into another app, message, prompt, note, etc. without opening Source and manually selecting everything.

Suggested UX

Add a Copy raw text item to the linked-file context/menu alongside Preview, Source, and Copy path.

For plain-text/source files, it should copy the exact file contents to the clipboard. For Markdown specifically, that means preserving all Markdown formatting characters.

Start at the iOS linked-file context menu, alongside the existing Preview, Source, and Copy path actions. Trace how the file's source contents are retrieved and how clipboard actions are handled. Done means Copy raw text is available for linked files and preserves exact source contents, including Markdown syntax, rather than rendered preview text.