Add Overview tab with system vitals and replace WhyRating tab

- Add /stats Python API endpoint on NUC (CPU, RAM, Swap, Disk, uptime, load avg)
- Add VitalsBar component in header showing CPU/RAM/Disk mini bars
- Add Overview as new default landing tab with system health, service summary,
  recent deployments, quick links, and WhyRating project status
- Poll system stats every 30s, deployments every 30s on overview tab
- Remove standalone WhyRating tab (content moved to Overview)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/lib/stats.ts

@@ -0,0 +1,40 @@
+export interface SystemStats {
+  cpu_percent: number;
+  ram_total_mb: number;
+  ram_used_mb: number;
+  ram_percent: number;
+  swap_total_mb: number;
+  swap_used_mb: number;
+  swap_percent: number;
+  disk_total_gb: number;
+  disk_used_gb: number;
+  disk_percent: number;
+  uptime_seconds: number;
+  load_avg: [number, number, number];
+}
+
+export function getVitalsColor(percent: number): string {
+  if (percent >= 90) return 'text-red-500';
+  if (percent >= 70) return 'text-amber-500';
+  return 'text-emerald-500';
+}
+
+export function getVitalsBg(percent: number): string {
+  if (percent >= 90) return 'bg-red-500';
+  if (percent >= 70) return 'bg-amber-500';
+  return 'bg-emerald-500';
+}
+
+export function getVitalsTrack(percent: number): string {
+  if (percent >= 90) return 'bg-red-500/20';
+  if (percent >= 70) return 'bg-amber-500/20';
+  return 'bg-emerald-500/20';
+}
+
+export function formatUptime(seconds: number): string {
+  const days = Math.floor(seconds / 86400);
+  const hours = Math.floor((seconds % 86400) / 3600);
+  if (days > 0) return `${days}d ${hours}h`;
+  const mins = Math.floor((seconds % 3600) / 60);
+  return `${hours}h ${mins}m`;
+}