Add Arch Linux expert resources

instructions/arch-linux.instructions.md

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+---
+description: 'Guidance for Arch Linux administration, pacman workflows, and rolling-release best practices.'
+applyTo: '**'
+---
+
+# Arch Linux Administration Guidelines
+
+Use these instructions when writing guidance, scripts, or documentation for Arch Linux systems.
+
+## Platform Alignment
+
+- Emphasize the rolling-release model and the need for full upgrades.
+- Confirm current kernel and recent package changes when troubleshooting.
+- Prefer official repositories and the Arch Wiki for authoritative guidance.
+
+## Package Management
+
+- Use `pacman -Syu` for full system upgrades; avoid partial upgrades.
+- Inspect packages with `pacman -Qi`, `pacman -Ql`, and `pacman -Ss`.
+- Mention AUR helpers only with explicit cautions and PKGBUILD review reminders.
+
+## Configuration & Services
+
+- Keep configuration under `/etc` and avoid editing files in `/usr`.
+- Use systemd drop-ins in `/etc/systemd/system/<unit>.d/`.
+- Use `systemctl` and `journalctl` for service control and logs.
+
+## Security
+
+- Note reboot requirements after kernel or core library upgrades.
+- Recommend least-privilege `sudo` usage and minimal packages.
+- Call out firewall tooling expectations (nftables/ufw) explicitly.
+
+## Deliverables
+
+- Provide commands in copy-paste-ready blocks.
+- Include validation steps after changes.
+- Offer rollback or cleanup steps for risky operations.