feat: dark/light mode + trading console BI + Chart.js local + fix themeScript

- Dark/light mode toggle across all pages (login, dashboard, corporate, admin, BI)
- BI Executive redesigned as permanent dark trading console (Bloomberg-style)
- Floating vertical nav with anchor scroll for mobile navigation
- Chart.js bundled locally (eliminates CDN dependency)
- Chart.js inlined in HTML for guaranteed loading
- Fix: themeScript </script> tag had literal backslash breaking HTML parser
- Fix: each chart wrapped in individual try/catch for graceful degradation
- No-cache headers on BI page to prevent stale HTML
- Robust init that handles DOMContentLoaded already fired

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server.js

@@ -328,6 +328,8 @@ app.get('/admin/dashboard', requireRole('admin'), (req, res) => {
 // --- Admin BI Dashboard (admin only) ---
 app.get('/admin/bi', requireRole('admin'), (req, res) => {
   try {
+    res.set('Cache-Control', 'no-store, no-cache, must-revalidate');
+    res.set('Pragma', 'no-cache');
     const html = buildAdminBIHTML(req.session.user);
     res.send(html);
   } catch (err) {