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

views/pages/quick.ejs

@@ -47,7 +47,7 @@
     <div class="lt-form-group">
       <label class="lt-label" for="qc-command">Command</label>
       <textarea class="lt-textarea" id="qc-command" rows="4" placeholder="Enter command to execute (e.g. 'uptime' or 'df -h')"></textarea>
-      <div class="lt-field-hint">Ctrl+Enter to execute</div>
+      <div class="lt-form-hint">Ctrl+Enter to execute</div>
     </div>
 
     <button type="submit" class="lt-btn lt-btn-primary" id="qc-execute-btn">&#x25b6; Execute Command</button>