fix(guest): add us-acentos keyboard layout option

[dyl-joseph]

Why

Try Omarchy runs on Macs with ANSI keyboards. The onboarding list offered only br-abnt2 for Brazilian Portuguese. That layout puts semicolon on the key labeled slash. ANSI hardware has no AB11 key. This change adds us-acentos. It maps to XKB us with the intl variant. Accents work through dead keys. Slash stays on its printed key.

Scope

• guest/patches/omarchy/keyboard-us-acentos.patch adds one row to OMARCHY_KEYBOARD_LAYOUTS.
• guest/spec.json registers the keyboard-us-acentos backport.
• guest/tests/verify.py requires the backport and checks patch content.
• guest/packages.lock.json refreshes the ARM64 lock to current repos.

Tradeoffs

Upstream owns the list. A backport keeps the pinned tree verbatim and applies one reviewed row. A label that names Portuguese and Brazil would read better for Brazilians. The issue requests the English US intl wording. This keeps the requested wording so upstream can adopt the same row.

Blast Radius

The first boot picker gains one entry. Existing entries keep their order and values. apply_keyboard and input.lua stay unchanged. systemd-firstboot resolves us-acentos through kbd-model-map.

Verification

• Pinned file has zero us-acentos rows before. It has one after.
• git apply check passes with whitespace error on.
• apply-omarchy-backports.py applies the backport and the digest matches.
• Guest backport unit tests pass with 5 tests.
• guest/tests/verify.py fails on the red commit and passes on green.
• Booted the built guest on an Apple Silicon Mac. Picked English (US, intl. with dead keys) at onboarding. Typed /, ', e for é, ', c for ç, ~, a for ã, ^, a for â, and ', space for a literal quote. All matched.

Fixes #194.