feat(ui): TDS migration stage 3 — integration fixes, legacy removal, docs

- Fix design-system class names that do not exist in base.css (.lt-alert--error,
  .lt-form-hint); add shared .lt-modal-lg, .lt-field-error and .is-invalid rules
- Remove public/index.html and the public/base.js symlink
- package.json: start script, correct main
- README: vendored design system, Web UI section, new env vars, read-only dev mode

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HamVMDrA8RqhyxmUHgiqRp

public/assets/pages/workflows.js

@@ -290,11 +290,11 @@
       var el = document.getElementById('wf-run-param-' + p.name);
       var val = el ? el.value.trim() : '';
       if (p.required && !val) {
-        el.classList.add('wf-input-invalid');
+        el.classList.add('is-invalid');
         el.focus();
         return;
       }
-      el && el.classList.remove('wf-input-invalid');
+      el && el.classList.remove('is-invalid');
       if (val) params[p.name] = val;
     }