music: re-enable background loop (default = playful) + profile on/off; coins 2000

- sound.ts: restored startMusic (was a no-op stub) playing the selected track
  through musicGain (in-game mute still applies); default track switched to
  "playful" (per user). Music auto-starts on init when enabled.
- Profile → Audio: re-added a music on/off toggle (so players can disable it
  outside the game too); SFX toggle unchanged.
- Economy tune: starting coins 1000 → 2000 (mock defaultProfile + server
  ProfileDto) so new players start a bit richer.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/screens/ProfileScreen.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import { motion } from "framer-motion";
-import { Check, ChevronLeft, Crown, Eye, EyeOff, Gift, Lock, LogOut, MapPin, Pencil, Search, Star, Upload, Users, Volume2 } from "lucide-react";
+import { Check, ChevronLeft, Crown, Eye, EyeOff, Gift, Lock, LogOut, MapPin, Music, Pencil, Search, Star, Upload, Users, Volume2 } from "lucide-react";
 import { useRef, useState } from "react";
 import { ScreenHeader, ScreenShell } from "@/components/online/ScreenHeader";
 import { RankBadge } from "@/components/online/RankBadge";
@@ -667,11 +667,12 @@ function CityRewardCard() {
 
 function SoundSettings() {
   const { t } = useI18n();
-  const { sfx, toggleSfx } = useSoundStore();
+  const { sfx, toggleSfx, music, toggleMusic } = useSoundStore();
   return (
     <div className="panel rounded-2xl p-4">
       <h3 className="text-sm font-bold text-cream/80 mb-2">{t("settings.audio")}</h3>
       <ToggleRow icon={<Volume2 className="size-4 text-gold-400" />} label={t("settings.sound")} on={sfx} onClick={toggleSfx} />
+      <ToggleRow icon={<Music className="size-4 text-gold-400" />} label={t("settings.music")} on={music} onClick={toggleMusic} />
     </div>
   );
 }