fix(desktop): restore clipboard shortcuts and edit context menu

[jk2lx]

Summary

• Menu.setApplicationMenu(null) was removing the Edit roles, so Cmd/Ctrl+C/V/X did nothing in the desktop app (especially noticeable on macOS).
• Electron also does not show a right-click edit menu by default, so paste/copy from the OS menu/context menu was missing in inputs.
• Adds a small application Edit menu again, and an in-page context menu for editable fields / log text that picks up the same paper colours as the existing MUI menus.
• Limits drag-select to inputs, textareas, and similar text surfaces so you cannot highlight the whole chrome by accident.

Test plan

• Build/run the desktop app on macOS
• Confirm Cmd+C / Cmd+V / Cmd+X work in text fields
• Right-click an input → Cut/Copy/Paste appear and work
• Right-click log output → Copy / Select All
• Check light and dark theme: menu should look like the explorer/canvas menus, not pure white
• Labels/buttons in the UI should not be drag-selectable

@FloSch62 Could you please review this PR?