Rich per-player stats + pick-your-metric leaderboard

- lib/player-stats.ts: single computePlayerStats() reads every
  world/stats/<uuid>.json plus world/advancements/<uuid>.json and joins
  with usercache.json. Returns a flat PlayerStats record per player:
  playtime, longest life, mob/player kills, deaths, K/D, damage dealt
  and taken (HP-scaled), blocks mined, items used / crafted / picked up
  (+ unique), distance (summed across all _one_cm stats), chest opens,
  nether/end trips, villager trades, fish caught, animals bred, and
  advancements (non-recipe) / recipes unlocked.
- New GET /api/players/stats (authed, 60s memo). Existing
  /api/players/playtime now returns a thin projection of the same
  computed data (shared cache key keeps both endpoints cheap).
- New components/Leaderboard.tsx with a metric select grouped into
  Time / Combat / World / Exploration / Progression / Economy (22
  metrics). Sorts descending, top 10 with "show all" toggle, smart
  number formatting (1.2k / 3.4M / HP / km). Replaces the old
  PlaytimeLeaderboard in the Players tab.
- PlayerDrawer upgraded: uses the full stats payload, shows small
  tiles for Kills / Deaths / K/D / Advs / Mined / Crafted / Distance
  alongside Playtime + Last seen.

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

components/PlayerManager.tsx

@@ -15,7 +15,7 @@ import {
   CardTitle,
 } from "@/components/ui/card";
 import { PlayerAvatar } from "@/components/PlayerAvatar";
-import { PlaytimeLeaderboard } from "@/components/PlaytimeLeaderboard";
+import { Leaderboard } from "@/components/Leaderboard";
 
 type PlayerData = {
   ops: { name: string; uuid: string; level: number }[];
@@ -129,7 +129,7 @@ export function PlayerManager() {
 
   return (
     <div className="space-y-4 sm:space-y-6">
-      <PlaytimeLeaderboard />
+      <Leaderboard />
     <Card>
       <CardHeader>
         <CardTitle>Player Management</CardTitle>