feat(flake): expose nixosModules.omnixy core aggregate

Extract the reusable core module list into modules/default.nix (single
source of truth) and expose it as nixosModules.omnixy / .default.
configuration.nix now imports ./modules instead of listing each module,
so this repo's hosts and external consumers share one definition. Theme
stays a settings.theme-driven import inside the aggregate. Packs,
dev-env, sops and home-manager remain injected by mkSystem.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

configuration.nix

@@ -15,28 +15,14 @@ let
 in
 {
   imports = [
-    # NOTE: hardware-configuration.nix is imported per-host from
-    # hosts/<name>/default.nix (it's machine-specific), not here.
-
-    # Omnixient modules
-    ./modules/lib.nix
-    ./modules/core.nix
-    ./modules/colors.nix
-    ./modules/boot.nix
-    ./modules/security.nix
-    ./modules/secrets.nix
-    ./modules/fastfetch.nix
-    ./modules/walker.nix
-    ./modules/scripts.nix
-    ./modules/menus.nix
-    ./modules/desktop/hyprland.nix
-    ./modules/packages.nix
-    ./modules/development.nix
-    ./modules/mcp.nix
-    ./modules/themes/${currentTheme}.nix
-    ./modules/users.nix
-    ./modules/services.nix
-    ./modules/hardware
+    # Omnixient core module aggregate (modules/default.nix) — the same set
+    # exposed as nixosModules.omni for external consumers, so there's a
+    # single source of truth for the core module list. The active theme
+    # is selected inside it from settings.theme.
+    #
+    # hardware-configuration.nix is imported per-host from
+    # hosts/<name>/default.nix (machine-specific), not here.
+    ./modules
   ];
 
   # --- Per-host settings (edit these) ---