Enable unsigned desktop release builds for PoC

[earayu]

Why

We need installable macOS and Windows Desktop artifacts for the ApeMind Agent PoC before signing certificates are available.

What changed

• Enable macOS Apple Silicon and Intel Desktop release jobs with signing: false.
• Disable macOS quick launch checks for release artifacts to avoid unsigned-app launch noise in CI.
• Enable Windows standard and CUDA Desktop release jobs with signing: false.
• Make the final release job wait for macOS, Linux, and Windows Desktop artifacts so they are uploaded to the GitHub release.

What this does not solve

• No Apple notarization or Windows Authenticode signing.
• Users may see OS security warnings when opening these PoC builds.
• Formal external distribution still needs signing secrets and signed release jobs.

Validation

• git diff --check