remove agenix and migrate secrets to clan vars

squash this

modules/gandi.nix

@@ -0,0 +1,15 @@
+{
+  clan.core.vars.generators.gandi = {
+    prompts.gandi-token = {
+      description = "gandi access token";
+      type = "hidden";
+    };
+    files.gandi-env = {
+      secret = true;
+    };
+    script = ''
+      printf %s "GANDIV5_PERSONAL_ACCESS_TOKEN=" >> $out/gandi-env
+      cat $prompts/gandi-token >> $out/gandi-env
+    '';
+  };
+}