move swagger-ui-theme/ out of hive-c0re/

hive-c0re doesn't touch these files anymore (nginx hosts them
directly, see the previous commit) — hive-c0re/swagger-ui-theme/ was
a leftover from the original SWAGGER_UI_OVERWRITE_FOLDER build-hook
design, which this PR moved away from. New location matches the
existing top-level-directory-for-nix-packaged-assets convention
(branding/, claude-plugins/).

Pure rename, no content change: nix/packages/swagger-ui-theme.nix's
three file references updated, everything else picks it up from the
same content hash (nix build .#swagger-ui-theme resolves to the exact
same store path as before the move).

swagger-ui-theme/swagger-initializer.js

@@ -0,0 +1,21 @@
+window.onload = function() {
+  //<editor-fold desc="Changeable Configuration Block">
+
+  // the following lines will be replaced by docker/configurator, when it runs in a docker-container
+  window.ui = SwaggerUIBundle({
+    "dom_id": "#swagger-ui",
+  "url": "/api/openapi.json",
+  "deepLinking": true,
+  "layout": "StandaloneLayout",
+    presets: [
+      SwaggerUIBundle.presets.apis,
+      SwaggerUIStandalonePreset
+    ],
+    plugins: [
+      SwaggerUIBundle.plugins.DownloadUrl
+    ],
+
+  });
+
+  //</editor-fold>
+};