feat(ui): TDS migration stage 1 — EJS layout, CSP, vendored design system, shared runtime

- Vendor web_template base.css/base.js (v1.2 bbec859) under public/web_template with sync script
- Add views/layout.ejs (fixed upstream EJS comment delimiters, mobile drawer, cmd palette,
  keys help, WS status, theme toggle) and lib/render.js two-step renderer
- Add page routes for /, /workers, /workflows, /executions, /quick, /scheduler (stub views)
- helmet with strict nonce CSP (script-src-attr 'none'), /csp-report, report-only toggle
- lib/pageauth.js: shared users upsert + HTML 401/403 for page routes
- PULSE_DEV_READONLY guard disabling background writers for local testing
- public/assets/app.js shared runtime (Pulse namespace, delegated actions, WS singleton,
  themed confirm modal) and app.css
- eslint globals for browser files; ignore vendored assets

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

views/partials/keys-help.ejs

@@ -0,0 +1,23 @@
+  <!-- KEYBOARD SHORTCUTS MODAL -->
+  <div id="lt-keys-help" class="lt-modal-overlay" aria-hidden="true">
+    <div class="lt-modal" role="dialog" aria-modal="true" aria-labelledby="lt-keys-help-title">
+      <div class="lt-modal-header">
+        <span class="lt-modal-title" id="lt-keys-help-title">Keyboard Shortcuts</span>
+        <button type="button" class="lt-modal-close" data-modal-close aria-label="Close">&#x2715;</button>
+      </div>
+      <div class="lt-modal-body">
+        <table class="lt-table">
+          <thead><tr><th>Shortcut</th><th>Action</th></tr></thead>
+          <tbody>
+            <tr><td>Ctrl / &#x2318; + K</td><td>Command palette</td></tr>
+            <tr><td>R</td><td>Refresh data</td></tr>
+            <tr><td>?</td><td>Show this help</td></tr>
+            <tr><td>ESC</td><td>Close modal / drawer / palette</td></tr>
+          </tbody>
+        </table>
+      </div>
+      <div class="lt-modal-footer">
+        <button type="button" class="lt-btn" data-modal-close>Close</button>
+      </div>
+    </div>
+  </div>