Homebrew cask is now deprecated because CopyQ fails Gatekeeper checks

**Is your feature request related to a problem? Please describe.**
Homebrew now warns that the `copyq` cask is deprecated because the app does not pass macOS Gatekeeper checks, and the warning says the cask will be disabled on `2026-09-01`.

That makes signing/notarization more than a UX issue now: it also threatens the continued availability of the official Homebrew install path for macOS users.

Current `brew install --cask copyq` output on macOS includes:

```text
Warning: copyq has been deprecated because it does not pass the macOS Gatekeeper check! It will be disabled on 2026-09-01.
==> Caveats
copyq is not signed and requires Accessibility access,
so you will need to re-grant Accessibility access every time the app is updated.
```

A related runtime/install issue is already tracked in `#2652`, but this separate issue is specifically about the Homebrew deprecation and distribution impact.

**Describe the solution you'd like**
Please make the macOS distribution pass Gatekeeper checks, ideally through proper code signing and notarization for release artifacts used by Homebrew.

That would:
- remove the current deprecation warning
- avoid the planned cask disable date
- improve first-run trust and installation UX for macOS users
- reduce the need for manual workarounds like ad-hoc signing or quarantine removal

**Describe alternatives you've considered**
Users can work around this locally with quarantine removal and ad-hoc signing, but that is brittle, not ideal for less technical users, and does not solve the Homebrew cask deprecation itself.

**Additional context**
Related issue: `#2652`