feat: add PC monitoring tab with Windows agent

- New /api/pc endpoints (heartbeat, list, delete)
- Dashboard tabs: Серверы / ПК with auto-refresh
- PowerShell agent: CPU, RAM, Disk, Network, GPU, Top processes
- One-command Windows installer with Scheduled Task
- PC setup instructions modal

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

server/static/css/style.css

@@ -600,6 +600,39 @@ main {
     overflow: hidden;
 }
 
+/* Tabs */
+.tabs {
+    display: flex;
+    gap: 4px;
+    margin-bottom: 20px;
+    background: var(--bg-card);
+    border: 1px solid var(--border);
+    border-radius: 10px;
+    padding: 4px;
+}
+
+.tab {
+    flex: 1;
+    padding: 10px 16px;
+    border: none;
+    border-radius: 8px;
+    background: transparent;
+    color: var(--text-secondary);
+    font-size: 14px;
+    font-weight: 600;
+    cursor: pointer;
+    transition: all 0.2s;
+}
+
+.tab:hover {
+    color: var(--text-primary);
+}
+
+.tab.active {
+    background: var(--accent);
+    color: white;
+}
+
 /* Footer */
 .app-footer {
     text-align: center;