fix(desktop): remove second Dock icon

[elijah-potter]

Issues

Fixes #3499

Description

Prevents the Harper Desktop highlighter helper from appearing as a second macOS app.

The highlighter runs in a child process with its own winit event loop. On macOS, that made the helper process show up separately in the Dock/app switcher with the default minimal app menu. This updates the highlighter event-loop setup to use macOS accessory activation policy and disables the default highlighter process menu, while leaving the main Harper Desktop app behavior unchanged.

Demo

N/A

How Has This Been Tested?

Manually.

AI Disclosure

• I am a human and didn't use any AI.
• I used LLM features of my editor, but not an agent.
• I used an AI agent interactively.
• I am an agent or I got an agent to do the work autonomously.

If Your PR Implements or Enhances a Linter

• I made up the sentences in the unit tests.
• The sentences in the unit tests were generated by an AI.
• I'm using examples from the bug report / feature request.
• I collected real-world sentences for the unit tests.

Checklist

• I have performed a self-review of my own code
• I have added tests to cover my changes
• I have considered splitting this into smaller pull requests.

[hippietrail]

This looks right. I never used winit but in a native AppKit app it's the activation policy.