Per-player playtime tracking + sparkline hover tooltips

- New GET /api/players/playtime (authed): reads each vanilla stats file
  under /home/minecraft/server/world/stats and maps uuid→name via
  usercache.json. Returns playtime in ticks and hours, plus file mtime
  as "last seen". Memoized 60s via lib/cache#memoAsync.
- New PlaytimeLeaderboard card in the Players tab:
    - Rank, avatar (click → PlayerDrawer), relative last-seen, hours.
    - Top 10 by default with toggle to show all; combined hours badge.
- PlayerDrawer surfaces the player's total hours + last-seen using the
  same cached playtime query, plus fills in UUID if the player is not
  in ops/whitelist/banned.
- lib/time.ts: formatHours() — minutes under 1h, "H.Hh" under a day,
  "Dd Hh" above.
- Analytics sparklines gain hover/touch tooltips:
    - Timestamps threaded through from each MetricEntry.
    - SVG overlay captures onMouseMove/onTouchMove, computes nearest
      index by x, draws a dashed guide line + focus dot.
    - Floating tooltip shows HH:MM + formatted value with unit; edge
      clamping keeps it in-frame at the extremes.
    - Per-chart formatValue so RAM shows GB, CPU 0 decimals, Players
      integer, TPS 1 decimal. Keeps the peak-player marker intact.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/time.ts

@@ -15,6 +15,19 @@ export function timeAgo(iso: string | number | Date): string {
   return `${yr}y ago`;
 }
 
+// Format a duration in hours as "H.Hh" under a day, otherwise "Dd Hh".
+export function formatHours(hours: number): string {
+  if (!isFinite(hours) || hours <= 0) return "0h";
+  if (hours < 1) {
+    const m = Math.round(hours * 60);
+    return `${m}m`;
+  }
+  if (hours < 24) return `${hours.toFixed(1)}h`;
+  const days = Math.floor(hours / 24);
+  const rem = Math.round(hours - days * 24);
+  return rem ? `${days}d ${rem}h` : `${days}d`;
+}
+
 export function formatBytes(n: number): string {
   if (!isFinite(n) || n <= 0) return "0 B";
   const units = ["B", "KB", "MB", "GB", "TB"];