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/server/fstab

@@ -0,0 +1,16 @@
+# Arcline Server — /etc/fstab template
+#
+# This is a TEMPLATE. btrfs-init.sh resolves the real root device UUID at
+# install/first-boot time and writes /etc/fstab. The subvolume layout matches
+# docs/btrfs.md.
+#
+# Device UUID is substituted by the installer.
+
+# <file system>  <mount point>  <type>  <options>                              <dump> <pass>
+UUID=__ROOT_UUID__ /             btrfs   rw,noatime,compress=zstd:3,subvol=@   0      0
+UUID=__ROOT_UUID__ /home         btrfs   rw,noatime,compress=zstd:3,subvol=@home 0    0
+UUID=__ROOT_UUID__ /var/log      btrfs   rw,noatime,compress=zstd:3,subvol=@log 0    0
+UUID=__ROOT_UUID__ /.snapshots   btrfs   rw,noatime,compress=zstd:3,subvol=@snapshots 0 0
+
+# swap
+/swap/swapfile                  none    swap    sw                          0      0