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>

public/login.html

@@ -4,6 +4,13 @@
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>BI - CCC | CambioReal</title>
+<script>
+  (function(){
+    var saved = localStorage.getItem('bi-theme');
+    var theme = saved || (window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light');
+    document.documentElement.setAttribute('data-theme', theme);
+  })();
+</script>
 <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&display=swap" rel="stylesheet">
 <style>
   :root {
@@ -137,6 +144,24 @@
     color: var(--text-secondary);
   }
 
+  /* Dark Mode */
+  [data-theme="dark"] {
+    --bg: #0D1117;
+    --card: #161B22;
+    --text: #E6EDF3;
+    --text-secondary: #B1BAC4;
+    --border: #30363D;
+    --error-bg: #3D1215;
+  }
+  [data-theme="dark"] .form-group input {
+    background: var(--bg);
+    color: var(--text);
+    border-color: var(--border);
+  }
+  [data-theme="dark"] .login-card {
+    box-shadow: 0 4px 24px rgba(0,0,0,0.3);
+  }
+
   /* Mobile responsive */
   @media (max-width: 480px) {
     .login-container { padding: 16px; }