feat(audio,site): calm santoor default music + card-fan logo site redesign

- audio: default background music is now the santoor track (calm Persian),
  rebuilt as a real plucked-santoor loop — fast metallic attack, shimmer
  overtones, soft tonic drone, longer Dastgah-e-Shur phrase
- site: marketing logo is now the app's card-fan icon (Logo.tsx + icon.svg);
  hero features the big logo with gold halo, floating suit motifs, and
  polished section dividers

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/sound.ts

@@ -38,7 +38,7 @@ class SoundManager {
   sfxEnabled = loadBool(LS_SFX);
   musicEnabled = loadBool(LS_MUSIC);
   musicTrack: MusicTrack =
-    (typeof window !== "undefined" && (localStorage.getItem(LS_TRACK) as MusicTrack)) || "playful";
+    (typeof window !== "undefined" && (localStorage.getItem(LS_TRACK) as MusicTrack)) || "santoor";
 
   /** Must be called from a user gesture to unlock audio. */
   init() {
@@ -198,11 +198,22 @@ class SoundManager {
   //  • playful — bouncy major-pentatonic staccato loop (UNO-like).
   private TRACKS: Record<
     MusicTrack,
-    { notes: number[]; gap: number; type: OscillatorType; attack: number; dur: number; peak: number; fifth: boolean }
+    {
+      notes: number[]; gap: number; type: OscillatorType; attack: number; dur: number;
+      peak: number; fifth: boolean;
+      shimmer?: boolean;  // bright metallic overtones — santoor pluck character
+      bassHz?: number;    // soft sustained tonic drone underneath
+    }
   > = {
     santoor: {
-      notes: [293.66, 311.13, 392, 440, 466.16, 392, 311.13, 293.66],
-      gap: 900, type: "sine", attack: 0.3, dur: 1.6, peak: 0.5, fifth: true,
+      // Dastgah-e Shur on D — a calm phrase that rises then settles, looping
+      // seamlessly. Plucked (fast attack, long decay) with metallic shimmer.
+      notes: [
+        293.66, 349.23, 392.0, 440.0, 392.0, 349.23, 311.13, 293.66,
+        349.23, 392.0, 466.16, 440.0, 392.0, 349.23, 311.13, 293.66,
+      ],
+      gap: 470, type: "triangle", attack: 0.004, dur: 1.15, peak: 0.4,
+      fifth: false, shimmer: true, bassHz: 73.42, // D2 drone
     },
     playful: {
       notes: [523.25, 659.25, 784, 659.25, 587.33, 698.46, 880, 698.46, 587.33, 523.25],
@@ -218,23 +229,35 @@ class SoundManager {
       if (!this.ctx || !this.musicGain) return;
       const cfg = this.TRACKS[this.musicTrack];
       const now = this.ctx.currentTime;
-      const freq = cfg.notes[this.step % cfg.notes.length];
+      const idx = this.step % cfg.notes.length;
+      const freq = cfg.notes[idx];
       this.step++;
-      const voice = (f: number, scale = 1) => {
+      const voice = (f: number, scale = 1, type = cfg.type, attack = cfg.attack, dur = cfg.dur) => {
         const osc = this.ctx!.createOscillator();
         const g = this.ctx!.createGain();
-        osc.type = cfg.type;
+        osc.type = type;
         osc.frequency.value = f;
         g.gain.setValueAtTime(0.0001, now);
-        g.gain.linearRampToValueAtTime(cfg.peak * scale, now + cfg.attack);
-        g.gain.exponentialRampToValueAtTime(0.0001, now + cfg.dur);
+        g.gain.linearRampToValueAtTime(cfg.peak * scale, now + attack);
+        g.gain.exponentialRampToValueAtTime(0.0001, now + dur);
         osc.connect(g);
         g.connect(this.musicGain!);
         osc.start(now);
-        osc.stop(now + cfg.dur + 0.05);
+        osc.stop(now + dur + 0.05);
       };
       voice(freq);
       if (cfg.fifth) voice(freq * 1.5, 0.45); // soft fifth above
+      if (cfg.shimmer) {
+        // Metallic santoor overtones: a brighter octave + a faint third partial,
+        // both with quick decay so the pluck shimmers then fades.
+        voice(freq * 2, 0.16, "sine", 0.003, cfg.dur * 0.55);
+        voice(freq * 3, 0.06, "sine", 0.003, cfg.dur * 0.4);
+      }
+      // Soft sustained tonic drone re-struck once per phrase half.
+      if (cfg.bassHz && idx % (cfg.notes.length / 2) === 0) {
+        const span = (cfg.gap / 1000) * (cfg.notes.length / 2);
+        voice(cfg.bassHz, 0.5, "sine", 0.25, span * 0.95);
+      }
     };
     tick();
     this.musicTimer = setInterval(tick, this.TRACKS[this.musicTrack].gap);