nix: reorganize

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

nix/default.nix

@@ -0,0 +1,18 @@
+{ ... }: {
+  imports = [
+    ./torana.nix
+    ./torana-web.nix
+  ];
+
+  perSystem = { self', pkgs, ... }: {
+    packages.default = self'.packages.torana;
+
+    devShells.default = pkgs.mkShell {
+      name = "torana-dev";
+      inputsFrom = with self'.devShells; [
+        torana
+        torana-web
+      ];
+    };
+  };
+}