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

package.json

@@ -1,8 +1,9 @@
 {
   "name": "pulse-server",
   "version": "1.0.0",
-  "main": "index.js",
+  "main": "server.js",
   "scripts": {
+    "start": "node server.js",
     "test": "jest --coverage"
   },
   "keywords": [],