[Feature] Add additional CLI commands

Summary

Add a few additional CLI commands for use from external apps, scripts and browsers

Problem it solves

This would facilitate communication between Marktext and other applications/scripts

Proposed solution

Additional commands

• --note PATH_TO_NOTE
  • Open supplied note path/filename
  • Create the note if it does not exist
• --text TEXT_STRING
  • Text to add to the previous suggested --note command
• --clipboard
  • Text from the clipboard to add to the previous suggested --note command
• --append_header HEADER_STRING
  • Append supplied text to the bottom of text after supplied header
• --prepend_header HEADER_STRING
  • Prepend supplied text to the top of text after supplied header

Other Possibilities

• --image FILE
  • Image to add to the Global image folder
• --attachment FILE
  • This would be useful for other non image file types Eg. PDF, XML, CVS, etc.
  • This would probably work best with an option for a Global attachments folder: location in settings

Alternatives considered [optional]

A lot of this could be accomplished with bash scripts, but that would not always work as well from browsers and other apps

Additional context [optional]

Examples:

marktext --note /home/user/Documents/Marktext/Tasks.md --text "- [ ] Some important task" --append-header "Todo"

marktext --note /home/user/Documents/Marktext/Tasks.md --text "- [ ] Another important task" --prepend-header "Todo"

Result In Tasks.md

Todo

• Another important task
• Some important task

Another example using clipboard

marktext --note /home/user/Documents/Marktext/Research.md --clipboard --prepend-header "Project Research"

Result In Research.md

Project Research

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Start by locating MarkText's existing CLI argument entry point and any current command handling. Trace how a note path, text, clipboard content, and header operations would interact, then clarify behavior for missing files and the optional image or attachment proposals. Done means the agreed commands work with the documented examples and have coverage for their supported combinations.