feat: add server, workstation, and cloud edition manifests

Define the three flagship editions as plain-text manifests:

- server (bastion): production server - observability stack, containers.
- workstation (forge): curated KDE Plasma + dev toolchains.
- cloud (nimbus): cloud kernel, cloud-init, guest agents.

Each manifest carries metadata (services to enable/mask), a package
list, a hardened kernel cmdline, and a btrfs fstab template.

editions/cloud/metadata.yaml

@@ -0,0 +1,36 @@
+# Edition manifest: Arcline Cloud
+# Codename: nimbus
+edition: cloud
+codename: nimbus
+summary: Minimal base images optimized for cloud infrastructures.
+description: >
+  Designed for AWS, GCP, Azure, or your own private cloud. Uses the cloud
+  kernel, cloud-init for first-boot provisioning, and a networkd-first
+  network stack. Same hardening baseline as server.
+
+image:
+  type: iso
+  boot: bios+efi
+  filesystem: btrfs
+  compression: zstd:3
+
+packages:
+  extra_repos: []
+
+users:
+  - arcline
+
+services:
+  enabled:
+    - systemd-networkd
+    - systemd-resolved
+    - cloud-init
+    - cloud-init-local
+    - ssh
+    - nftables
+    - apparmor
+    - qemu-guest-agent
+    - arcline-snapshot.timer
+  masked:
+    - apt-daily.timer
+    - apt-daily-upgrade.timer