Address PR review: drop the zram Module, scope comments (task 0003)

Remove modules/zram.nix — it only wrapped the native zramSwap.enable toggle
without adding anything — and enable zram inline on neogaia instead. Rewrite
the touched comments to describe only the current file content, and record
the in-file-comment convention in CLAUDE.md.

modules/zram.nix

@@ -1,14 +0,0 @@
-{ config, lib, ... }:
-# A toggle for RAM-backed swap. A Host that has no on-disk swap partition (like
-# neogaia, whose disko layout deliberately omits one) enables this to get a
-# compressed zram device instead.
-let
-  cfg = config.modules.zram;
-in
-{
-  options.modules.zram.enable = lib.mkEnableOption "zram-backed compressed swap";
-
-  config = lib.mkIf cfg.enable {
-    zramSwap.enable = true;
-  };
-}