fix(devcontainer): use the main Ubuntu archive for ARM64 (#16363)

## Description

Fix ARM64 devcontainer builds that fail to install Playwright browser
dependencies because the ports archive lacks required packages.

Ubuntu 26.04 moved ARM64 packages to the main archive ([Ubuntu
announcement](https://discourse.ubuntu.com/t/ubuntu-on-arm-summer-26-update/84872)).
The pinned base image still uses ports. Update its ARM64 repository URL
before installing packages. Other architectures keep their existing
sources.

The main archive contains matching `xvfb` and `xserver-common` packages.
This change uses normal Ubuntu package downloads and signature
verification.

## How Has This Been Tested?

- Verified ARM64 package index hashes against published InRelease
metadata.
- Downloaded matching `xvfb` and `xserver-common` packages and verified
their hashes.
- Pre-commit checks passed.
- [Fresh ARM64 devcontainer CI build
passed](https://github.com/onyx-dot-app/onyx/actions/runs/39534888216/job/119009199000)
in 6 minutes. Playwright dependencies installed in 15.7 seconds,
including matching `xvfb` and `xserver-common` packages.

## Additional Options

- [ ] [Optional] Please cherry-pick this PR to the latest release
version.

.devcontainer/Dockerfile

@@ -10,7 +10,11 @@ FROM ${BASE_IMAGE_REGISTRY}/library/node:24.16.0-trixie-slim@sha256:45fbb3ca3b6c
 
 FROM ${BASE_IMAGE_REGISTRY}/library/ubuntu:26.04@sha256:c098726dd9b9733f3e885f8de0ef375206a311b0a317eadc40d347b1115fb944
 
-RUN apt-get update && apt-get install -y --no-install-recommends \
+# Ubuntu 26.04 moved ARM64 packages from ports to the main archive.
+RUN if [ "$(dpkg --print-architecture)" = arm64 ]; then \
+    sed -i 's|ports.ubuntu.com/ubuntu-ports|archive.ubuntu.com/ubuntu|g' /etc/apt/sources.list.d/ubuntu.sources; \
+  fi \
+  && apt-get update && apt-get install -y --no-install-recommends \
   build-essential \
   ca-certificates \
   cargo \