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/dashboard.js

@@ -139,12 +139,23 @@
   /* -------------------------------------------------------------------
      Data loading
      ------------------------------------------------------------------- */
+  /* Toast a load failure at most once per outage, so the 30 s auto-refresh
+     does not stack a toast every cycle while the API is down. */
+  let _loadFailed = false;
+  function reportLoadError(what, e) {
+    console.error('[Pulse:dashboard] failed to load ' + what, e);
+    if (_loadFailed) return;
+    _loadFailed = true;
+    if (Pulse.toast) Pulse.toast.error((e && e.message) || ('Failed to load ' + what));
+  }
+
   async function loadWorkers() {
     try {
       _workers = await Pulse.api.get('/api/workers') || [];
+      _loadFailed = false;
     } catch (e) {
       _workers = [];
-      console.error('[Pulse:dashboard] failed to load workers', e);
+      reportLoadError('workers', e);
     }
     renderWorkers(_workers);
     return _workers;
@@ -156,7 +167,7 @@
       _executions = (data && data.executions) || [];
     } catch (e) {
       _executions = [];
-      console.error('[Pulse:dashboard] failed to load executions', e);
+      reportLoadError('executions', e);
     }
     renderExecutions(_executions);
     return _executions;