Associate Kromacut files with the desktop app

If Kromacut is distributed as a desktop app, Kromacut-owned file types should be associated with the app at the operating-system level.

The goal is for users to recognize and open Kromacut files naturally from their file manager, instead of needing to open the app first and manually import them.

Useful outcomes:

• Kromacut file types use a recognizable Kromacut icon in the OS file browser.
• Double-clicking a supported Kromacut file opens Kromacut.
• When possible, the app should open or import the selected file directly.
• The association should apply only to Kromacut-specific file formats, not generic image or model formats unless there is a clear reason.
• Desktop installers should register the association cleanly for the supported platforms.

This is mainly a polish and usability improvement for the desktop app experience. It makes saved presets, profiles, projects, or other Kromacut-specific files feel like first-class app documents.

Start by locating the Tauri desktop configuration and installer entry points, then identify Kromacut-specific file formats and how selected files reach the app. Done means supported platforms register only those formats, show a Kromacut icon, and open or import files through the desktop app.