Restructure into a multi-machine flake and add the enzo laptop

Split the single-host config into a shared minimal base plus opt-in
profiles, and add a second machine (enzo laptop) alongside kusanagi.

- flake: add mkMachine helper; declare nixosConfigurations.kusanagi and
  .enzo; add the disko input; move overlays per-machine.
- common/: minimal base only (boot, networking, tailscale, locale, nix
  settings, neovim editor). Old configuration.nix/programs.nix removed.
- profiles/: coarse opt-in bundles (desktop, dev, apps). kusanagi imports
  all three and stays byte-for-byte identical to the running system.
- machines/kusanagi/: all workstation-only config (ROCm, Scarlett audio,
  optical-disc archiving, NAS mounts, kavita/immich/ollama); hardware
  config moved here unchanged. User stays 'henz'.
- machines/enzo/: new laptop. Declarative LUKS+btrfs via disko
  (LVM-on-LUKS, TPM2+PIN unlock, zram + encrypted swap for
  suspend-then-hibernate); its own minimal niri desktop with
  playback-only audio (no rtkit/jack); user 'hwebs'.

Assisted-by: Claude:claude-opus-4-8

1 files changed, 9 insertions, 0 deletions

diff --git a/common/default.nix b/common/default.nix
new file mode 100644
index 0000000..946b3a7
--- /dev/null
+++ b/common/default.nix
@@ -0,0 +1,9 @@
+# Configuration shared by all machines. Machine-specific settings live under
+# ../machines/<hostname>/default.nix.
+{ ... }:
+
+{
+  imports = [
+    ./core.nix
+  ];
+}