vars: use correct paths for value accesses

Use correct paths for value accesses of vars under:

- `per-machine`
- `shared`

clanModules/state-version/default.nix

@@ -0,0 +1,12 @@
+{ config, lib, ... }:
+{
+  system.stateVersion = config.clan.core.vars.generators.state-version.files.version.value;
+
+  clan.core.vars.generators.state-version = {
+    files.version.secret = false;
+    runtimeInputs = [ ];
+    script = ''
+      echo ${lib.versions.majorMinor lib.version} > $out/version
+    '';
+  };
+}