Correct M3 support briefing and reject unsupported M3 Ultra

[pkyanam]

This follow-up corrects stale M3 capability guidance in PR omacom#343.

The current bin/omarchy-mac-asahi-install text says sleep works and webcam support is missing, and bin/omarchy-mac-setup says Asahi has not released M3 support. Asahi's September 6 announcement now says M3 support is official behind Expert mode, webcam and microphones work, and sleep does not work because of the firmware framebuffer: https://asahilinux.org/2026/09/m2-episode-1/

I prepared a focused correction on top of this PR head (c52724f):

• installer briefing: webcam and video decoding are working; sleep is a limitation;
• guided setup warning: support is Expert-gated and sleep is unavailable;
• installer and guided setup: M3 Ultra is rejected as unsupported before any fetch or installer invocation;
• docs/apple-m3.md: update the dated capability summary and link the announcement;
• test/shell.d/apple-m3-test.sh: regression checks for the sleep status.

The focused Apple M3 test passes all 33 checks. Both changed scripts pass bash -n under macOS Bash 3.2, and git diff --check passes. Independent GPT-5.6-luna QA and review both passed the final commit; the QA evidence is in work/qa-m3-briefing-359c7c4.md in the local lab. This is a documentation, user-warning, and unsupported-model guard correction; it does not change the firmware allowlist or claim native graphics readiness. No installer, privilege, boot, partition, reboot, or physical-device operation was performed.

This change was prepared with AI-assisted development under the hardware owner’s authorization; the final patch and test claims were independently checked before publication.