feat: add multi-asset sidebar (BTC, USD, XAU) with asset switching

- Added sidebar navigation with 3 tabs: Bitcoin, Dólar, Ouro
- Added switchAsset() function to switch between assets
- Updated CSS with sidebar layout (fixed 200px sidebar)
- Updated script.js with asset state management
- Sync sidebar clock and status with main header
- BTC remains default active tab

static/style.css

@@ -15,27 +15,104 @@
     --shadow: 0 8px 32px rgba(0,0,0,0.4);
 }
 
-/* ── Reset & Base ───────────────────────────────────────── */
+/* ── Reset & Base ───────────────────────────────────── */
 * { margin: 0; padding: 0; box-sizing: border-box; }
+
+/* ── Sidebar Layout ──────────────────────────────────── */
 body {
+    display: flex;
+    min-height: 100vh;
     font-family: 'Exo 2', 'Noto Sans JP', sans-serif;
     background: var(--bg-dark);
     color: var(--text-primary);
-    min-height: 100vh;
     overflow-x: hidden;
 }
 
-/* ── Dashboard Layout ───────────────────────────────────── */
-.dashboard {
+/* ── Sidebar ─────────────────────────────────────────── */
+.sidebar {
+    width: 200px;
+    min-height: 100vh;
+    background: var(--bg-card);
+    border-right: 1px solid rgba(79,195,247,0.1);
+    display: flex;
+    flex-direction: column;
+    padding: 20px 0;
+    position: fixed;
+    left: 0;
+    top: 0;
+    bottom: 0;
+    z-index: 100;
+}
+.sidebar-logo {
+    display: flex;
+    align-items: center;
+    gap: 10px;
+    padding: 0 16px 20px;
+    border-bottom: 1px solid rgba(255,255,255,0.05);
+    margin-bottom: 20px;
+}
+.sidebar-logo-icon { font-size: 1.8rem; }
+.sidebar-logo-text { font-size: 0.9rem; line-height: 1.2; color: var(--text-primary); }
+.sidebar-logo-text strong { color: var(--accent-blue); }
+
+.sidebar-nav {
+    display: flex;
+    flex-direction: column;
+    gap: 4px;
+    padding: 0 10px;
+    flex: 1;
+}
+.sidebar-btn {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    gap: 2px;
+    padding: 14px 8px;
+    border: none;
+    border-radius: 12px;
+    background: transparent;
+    color: var(--text-secondary);
+    cursor: pointer;
+    transition: all 0.2s;
+    text-align: center;
+}
+.sidebar-btn:hover {
+    background: var(--bg-card-hover);
+    color: var(--text-primary);
+}
+.sidebar-btn.active {
+    background: rgba(79,195,247,0.1);
+    color: var(--accent-blue);
+    border: 1px solid rgba(79,195,247,0.2);
+}
+.sidebar-icon { font-size: 1.6rem; }
+.sidebar-label { font-size: 0.8rem; font-weight: 600; }
+.sidebar-pair { font-size: 0.65rem; opacity: 0.6; }
+
+.sidebar-footer {
+    padding: 16px;
+    border-top: 1px solid rgba(255,255,255,0.05);
+    text-align: center;
+}
+.sidebar-clock { font-size: 1.1rem; color: var(--accent-blue); margin-bottom: 8px; }
+.sidebar-status { display: flex; align-items: center; justify-content: center; gap: 6px; font-size: 0.75rem; color: var(--text-secondary); }
+
+/* ── Main Content ────────────────────────────────────── */
+.main-content {
+    margin-left: 200px;
+    flex: 1;
+    padding: 20px;
+    max-width: calc(100vw - 200px);
+}
+.main-content .dashboard {
     max-width: 1400px;
     margin: 0 auto;
-    padding: 20px;
     display: flex;
     flex-direction: column;
     gap: 24px;
 }
 
-/* ── Header ──────────────────────────────────────────────── */
+/* ── Header ──────────────────────────────────────────── */
 .header {
     display: flex;
     align-items: center;